--- /dev/null
+--- linux-4.18/fs/ext4/balloc.c 2019-11-28 14:55:26.506546036 +0300
++++ linux-4.18/fs/ext4/balloc.c 2019-12-02 11:21:50.565975537 +0300
+@@ -404,7 +404,8 @@ verified:
+ * Return buffer_head on success or NULL in case of failure.
+ */
+ struct buffer_head *
+-ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
++ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group,
++ int ignore_locked)
+ {
+ struct ext4_group_desc *desc;
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+@@ -435,6 +436,13 @@ ext4_read_block_bitmap_nowait(struct
+ if (bitmap_uptodate(bh))
+ goto verify;
+
++ if (ignore_locked && buffer_locked(bh)) {
++ /* buffer under IO already, do not wait
++ * if called for prefetching */
++ put_bh(bh);
++ return NULL;
++ }
++
+ lock_buffer(bh);
+ if (bitmap_uptodate(bh)) {
+ unlock_buffer(bh);
+@@ -524,7 +532,7 @@ ext4_read_block_bitmap(struct super_b
+ {
+ struct buffer_head *bh;
+
+- bh = ext4_read_block_bitmap_nowait(sb, block_group);
++ bh = ext4_read_block_bitmap_nowait(sb, block_group, 0);
+ if (!bh)
+ return NULL;
+ err = ext4_wait_block_bitmap(sb, block_group, bh);
+--- linux-4.18/fs/ext4/ext4.h 2019-11-28 14:55:26.470545343 +0300
++++ linux-4.18/fs/ext4/ext4.h 2019-12-02 11:21:40.795779972 +0300
+@@ -1446,6 +1446,8 @@ struct ext4_sb_info {
+ /* where last allocation was done - for stream allocation */
+ unsigned long s_mb_last_group;
+ unsigned long s_mb_last_start;
++ unsigned int s_mb_prefetch;
++ unsigned int s_mb_prefetch_limit;
+
+ /* stats for buddy allocator */
+ atomic_t s_bal_reqs; /* number of reqs with len > 1 */
+@@ -2401,7 +2403,8 @@ extern struct ext4_group_desc * ldisk
+ extern int ext4_should_retry_alloc(struct super_block *sb, int *retries);
+
+ extern struct buffer_head *ext4_read_block_bitmap_nowait(struct super_block *sb,
+- ext4_group_t block_group);
++ ext4_group_t block_group,
++ int ignore_locked);
+ extern int ext4_wait_block_bitmap(struct super_block *sb,
+ ext4_group_t block_group,
+ struct buffer_head *bh);
+--- linux-4.18/fs/ext4/mballoc.c 2019-11-28 14:55:26.500545920 +0300
++++ linux-4.18/fs/ext4/mballoc.c 2019-12-02 11:21:46.656897291 +0300
+@@ -868,7 +868,7 @@ static int ext4_mb_init_cache(struct
+ bh[i] = NULL;
+ continue;
+ }
+- if (!(bh[i] = ext4_read_block_bitmap_nowait(sb, group))) {
++ if (!(bh[i] = ext4_read_block_bitmap_nowait(sb, group, 0))) {
+ err = -ENOMEM;
+ goto out;
+ }
+@@ -2104,6 +2112,87 @@ static int ext4_mb_good_group(struct
+ return 0;
+ }
+
++/*
++ * each allocation context (i.e. a thread doing allocation) has own
++ * sliding prefetch window of @s_mb_prefetch size which starts at the
++ * very first goal and moves ahead of scaning.
++ * a side effect is that subsequent allocations will likely find
++ * the bitmaps in cache or at least in-flight.
++ */
++static void
++ext4_mb_prefetch(struct ext4_allocation_context *ac,
++ ext4_group_t start)
++{
++ struct super_block *sb = ac->ac_sb;
++ ext4_group_t ngroups = ext4_get_groups_count(sb);
++ struct ext4_sb_info *sbi = EXT4_SB(sb);
++ struct ext4_group_info *grp;
++ ext4_group_t group = start;
++ struct buffer_head *bh;
++ int nr;
++
++ /* limit prefetching at cr=0, otherwise mballoc can
++ * spend a lot of time loading imperfect groups */
++ if (ac->ac_criteria < 2 && ac->ac_prefetch_ios >= sbi->s_mb_prefetch_limit)
++ return;
++
++ /* batch prefetching to get few READs in flight */
++ nr = ac->ac_prefetch - group;
++ if (ac->ac_prefetch < group)
++ /* wrapped to the first groups */
++ nr += ngroups;
++ if (nr > 0)
++ return;
++ BUG_ON(nr < 0);
++
++ nr = sbi->s_mb_prefetch;
++ if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG)) {
++ /* align to flex_bg to get more bitmas with a single IO */
++ nr = (group / sbi->s_mb_prefetch) * sbi->s_mb_prefetch;
++ nr = nr + sbi->s_mb_prefetch - group;
++ }
++ while (nr-- > 0) {
++ grp = ext4_get_group_info(sb, group);
++ /* ignore empty groups - those will be skipped
++ * during the scanning as well */
++ if (grp->bb_free > 0 && EXT4_MB_GRP_NEED_INIT(grp)) {
++ bh = ext4_read_block_bitmap_nowait(sb, group, 1);
++ if (bh && !IS_ERR(bh)) {
++ if (!buffer_uptodate(bh))
++ ac->ac_prefetch_ios++;
++ brelse(bh);
++ }
++ }
++ if (++group >= ngroups)
++ group = 0;
++ }
++ ac->ac_prefetch = group;
++}
++
++static void
++ext4_mb_prefetch_fini(struct ext4_allocation_context *ac)
++{
++ struct ext4_group_info *grp;
++ ext4_group_t group;
++ int nr, rc;
++
++ /* initialize last window of prefetched groups */
++ nr = ac->ac_prefetch_ios;
++ if (nr > EXT4_SB(ac->ac_sb)->s_mb_prefetch)
++ nr = EXT4_SB(ac->ac_sb)->s_mb_prefetch;
++ group = ac->ac_prefetch;
++ while (nr-- > 0) {
++ grp = ext4_get_group_info(ac->ac_sb, group);
++ if (grp->bb_free > 0 && EXT4_MB_GRP_NEED_INIT(grp)) {
++ rc = ext4_mb_init_group(ac->ac_sb, group);
++ if (rc)
++ break;
++ }
++ if (group-- == 0)
++ group = ext4_get_groups_count(ac->ac_sb) - 1;
++ }
++}
++
+ static noinline_for_stack int
+ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
+ {
+@@ -2176,6 +2264,7 @@ repeat:
+ * from the goal value specified
+ */
+ group = ac->ac_g_ex.fe_group;
++ ac->ac_prefetch = group;
+
+ for (i = 0; i < ngroups; group++, i++) {
+ int ret = 0;
+@@ -2188,6 +2277,8 @@ repeat:
+ if (group >= ngroups)
+ group = 0;
+
++ ext4_mb_prefetch(ac, group);
++
+ /* This now checks without needing the buddy page */
+ ret = ext4_mb_good_group(ac, group, cr);
+ if (ret <= 0) {
+@@ -2260,6 +2351,8 @@ repeat:
+ out:
+ if (!err && ac->ac_status != AC_STATUS_FOUND && first_err)
+ err = first_err;
++ /* use prefetched bitmaps to init buddy so that read info is not lost */
++ ext4_mb_prefetch_fini(ac);
+ return err;
+ }
+
+@@ -2832,6 +2925,24 @@ int ext4_mb_init(struct super_block *
+ sbi->s_mb_large_req = sbi->s_stripe * 8;
+ sbi->s_mb_group_prealloc = sbi->s_stripe * 4;
+ }
++ if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG)) {
++ /* a single flex group is supposed to be read by a single IO */
++ sbi->s_mb_prefetch = 1 << sbi->s_es->s_log_groups_per_flex;
++ sbi->s_mb_prefetch *= 8; /* 8 prefetch IOs in flight at most */
++ } else {
++ sbi->s_mb_prefetch = 32;
++ }
++ if (sbi->s_mb_prefetch >= ext4_get_groups_count(sb))
++ sbi->s_mb_prefetch = ext4_get_groups_count(sb);
++ /* now many real IOs to prefetch within a single allocation at cr=0
++ * given cr=0 is an CPU-related optimization we shouldn't try to
++ * load too many groups, at some point we should start to use what
++ * we've got in memory.
++ * with an average random access time 5ms, it'd take a second to get
++ * 200 groups (* N with flex_bg), so let's make this limit 4 */
++ sbi->s_mb_prefetch_limit = sbi->s_mb_prefetch * 4;
++ if (sbi->s_mb_prefetch_limit > ext4_get_groups_count(sb))
++ sbi->s_mb_prefetch_limit = ext4_get_groups_count(sb);
+
+ sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
+ if (sbi->s_locality_groups == NULL) {
+--- linux-4.18/fs/ext4/mballoc.h 2019-11-28 14:55:26.471545362 +0300
++++ linux-4.18/fs/ext4/mballoc.h 2019-12-02 11:21:57.028104886 +0300
+@@ -177,6 +177,8 @@ struct ext4_allocation_context {
+ struct page *ac_buddy_page;
+ struct ext4_prealloc_space *ac_pa;
+ struct ext4_locality_group *ac_lg;
++ ext4_group_t ac_prefetch;
++ int ac_prefetch_ios; /* number of initialied prefetch IO */
+ };
+
+ #define AC_STATUS_CONTINUE 1
+--- linux-4.18/fs/ext4/super.c 2019-11-28 14:55:26.502545959 +0300
++++ linux-4.18/fs/ext4/super.c 2019-11-28 20:07:48.104558177 +0300
+@@ -190,6 +190,8 @@ EXT4_RW_ATTR_SBI_UI(msg_ratelimit_bur
+ EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
+ EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
+ EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
++EXT4_RW_ATTR_SBI_UI(mb_prefetch, s_mb_prefetch);
++EXT4_RW_ATTR_SBI_UI(mb_prefetch_limit, s_mb_prefetch_limit);
+ EXT4_DEPRECATED_ATTR(max_writeback_mb_bump, 128);
+ EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
+ EXT4_ATTR(trigger_fs_error, 0200, NULL, trigger_test_error);
+@@ -223,6 +224,8 @@ static struct attribute *ext4_attrs[]
+ ATTR_LIST(errors_count),
+ ATTR_LIST(first_error_time),
+ ATTR_LIST(last_error_time),
++ ATTR_LIST(mb_prefetch),
++ ATTR_LIST(mb_prefetch_limit),
+ NULL,
+ };
+
--- /dev/null
+--- linux-4.18/fs/ext4/balloc.c 2019-11-28 14:55:26.506546036 +0300
++++ linux-4.18/fs/ext4/balloc.c 2019-12-02 11:21:50.565975537 +0300
+@@ -404,7 +404,8 @@ verified:
+ * Return buffer_head on success or NULL in case of failure.
+ */
+ struct buffer_head *
+-ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
++ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group,
++ int ignore_locked)
+ {
+ struct ext4_group_desc *desc;
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+@@ -435,6 +436,13 @@ ext4_read_block_bitmap_nowait(struct
+ if (bitmap_uptodate(bh))
+ goto verify;
+
++ if (ignore_locked && buffer_locked(bh)) {
++ /* buffer under IO already, do not wait
++ * if called for prefetching */
++ put_bh(bh);
++ return NULL;
++ }
++
+ lock_buffer(bh);
+ if (bitmap_uptodate(bh)) {
+ unlock_buffer(bh);
+@@ -524,7 +532,7 @@ ext4_read_block_bitmap(struct super_b
+ struct buffer_head *bh;
+ int err;
+
+- bh = ext4_read_block_bitmap_nowait(sb, block_group);
++ bh = ext4_read_block_bitmap_nowait(sb, block_group, 0);
+ if (!bh)
+ return NULL;
+ err = ext4_wait_block_bitmap(sb, block_group, bh);
+--- linux-4.18/fs/ext4/ext4.h 2019-11-28 14:55:26.470545343 +0300
++++ linux-4.18/fs/ext4/ext4.h 2019-12-02 11:21:40.795779972 +0300
+@@ -1446,6 +1446,8 @@ struct ext4_sb_info {
+ /* where last allocation was done - for stream allocation */
+ unsigned long s_mb_last_group;
+ unsigned long s_mb_last_start;
++ unsigned int s_mb_prefetch;
++ unsigned int s_mb_prefetch_limit;
+
+ /* stats for buddy allocator */
+ atomic_t s_bal_reqs; /* number of reqs with len > 1 */
+@@ -2401,7 +2403,8 @@ extern struct ext4_group_desc * ldisk
+ extern int ext4_should_retry_alloc(struct super_block *sb, int *retries);
+
+ extern struct buffer_head *ext4_read_block_bitmap_nowait(struct super_block *sb,
+- ext4_group_t block_group);
++ ext4_group_t block_group,
++ int ignore_locked);
+ extern int ext4_wait_block_bitmap(struct super_block *sb,
+ ext4_group_t block_group,
+ struct buffer_head *bh);
+--- linux-4.18/fs/ext4/mballoc.c 2019-11-28 14:55:26.500545920 +0300
++++ linux-4.18/fs/ext4/mballoc.c 2019-12-02 11:21:46.656897291 +0300
+@@ -868,7 +868,7 @@ static int ext4_mb_init_cache(struct
+ bh[i] = NULL;
+ continue;
+ }
+- if (!(bh[i] = ext4_read_block_bitmap_nowait(sb, group))) {
++ if (!(bh[i] = ext4_read_block_bitmap_nowait(sb, group, 0))) {
+ err = -ENOMEM;
+ goto out;
+ }
+@@ -2104,6 +2112,87 @@ static int ext4_mb_good_group(struct
+ return 0;
+ }
+
++/*
++ * each allocation context (i.e. a thread doing allocation) has own
++ * sliding prefetch window of @s_mb_prefetch size which starts at the
++ * very first goal and moves ahead of scaning.
++ * a side effect is that subsequent allocations will likely find
++ * the bitmaps in cache or at least in-flight.
++ */
++static void
++ext4_mb_prefetch(struct ext4_allocation_context *ac,
++ ext4_group_t start)
++{
++ struct super_block *sb = ac->ac_sb;
++ ext4_group_t ngroups = ext4_get_groups_count(sb);
++ struct ext4_sb_info *sbi = EXT4_SB(sb);
++ struct ext4_group_info *grp;
++ ext4_group_t group = start;
++ struct buffer_head *bh;
++ int nr;
++
++ /* limit prefetching at cr=0, otherwise mballoc can
++ * spend a lot of time loading imperfect groups */
++ if (ac->ac_criteria < 2 && ac->ac_prefetch_ios >= sbi->s_mb_prefetch_limit)
++ return;
++
++ /* batch prefetching to get few READs in flight */
++ nr = ac->ac_prefetch - group;
++ if (ac->ac_prefetch < group)
++ /* wrapped to the first groups */
++ nr += ngroups;
++ if (nr > 0)
++ return;
++ BUG_ON(nr < 0);
++
++ nr = sbi->s_mb_prefetch;
++ if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG)) {
++ /* align to flex_bg to get more bitmas with a single IO */
++ nr = (group / sbi->s_mb_prefetch) * sbi->s_mb_prefetch;
++ nr = nr + sbi->s_mb_prefetch - group;
++ }
++ while (nr-- > 0) {
++ grp = ext4_get_group_info(sb, group);
++ /* ignore empty groups - those will be skipped
++ * during the scanning as well */
++ if (grp->bb_free > 0 && EXT4_MB_GRP_NEED_INIT(grp)) {
++ bh = ext4_read_block_bitmap_nowait(sb, group, 1);
++ if (bh && !IS_ERR(bh)) {
++ if (!buffer_uptodate(bh))
++ ac->ac_prefetch_ios++;
++ brelse(bh);
++ }
++ }
++ if (++group >= ngroups)
++ group = 0;
++ }
++ ac->ac_prefetch = group;
++}
++
++static void
++ext4_mb_prefetch_fini(struct ext4_allocation_context *ac)
++{
++ struct ext4_group_info *grp;
++ ext4_group_t group;
++ int nr, rc;
++
++ /* initialize last window of prefetched groups */
++ nr = ac->ac_prefetch_ios;
++ if (nr > EXT4_SB(ac->ac_sb)->s_mb_prefetch)
++ nr = EXT4_SB(ac->ac_sb)->s_mb_prefetch;
++ group = ac->ac_prefetch;
++ while (nr-- > 0) {
++ grp = ext4_get_group_info(ac->ac_sb, group);
++ if (grp->bb_free > 0 && EXT4_MB_GRP_NEED_INIT(grp)) {
++ rc = ext4_mb_init_group(ac->ac_sb, group);
++ if (rc)
++ break;
++ }
++ if (group-- == 0)
++ group = ext4_get_groups_count(ac->ac_sb) - 1;
++ }
++}
++
+ static noinline_for_stack int
+ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
+ {
+@@ -2176,6 +2264,7 @@ repeat:
+ * from the goal value specified
+ */
+ group = ac->ac_g_ex.fe_group;
++ ac->ac_prefetch = group;
+
+ for (i = 0; i < ngroups; group++, i++) {
+ int ret = 0;
+@@ -2188,6 +2277,8 @@ repeat:
+ if (group >= ngroups)
+ group = 0;
+
++ ext4_mb_prefetch(ac, group);
++
+ /* This now checks without needing the buddy page */
+ ret = ext4_mb_good_group(ac, group, cr);
+ if (ret <= 0) {
+@@ -2260,6 +2351,8 @@ repeat:
+ }
+ }
+ out:
++ /* use prefetched bitmaps to init buddy so that read info is not lost */
++ ext4_mb_prefetch_fini(ac);
+ return err;
+ }
+
+@@ -2832,6 +2925,24 @@ int ext4_mb_init(struct super_block *
+ sbi->s_mb_large_req = sbi->s_stripe * 8;
+ sbi->s_mb_group_prealloc = sbi->s_stripe * 4;
+ }
++ if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG)) {
++ /* a single flex group is supposed to be read by a single IO */
++ sbi->s_mb_prefetch = 1 << sbi->s_es->s_log_groups_per_flex;
++ sbi->s_mb_prefetch *= 8; /* 8 prefetch IOs in flight at most */
++ } else {
++ sbi->s_mb_prefetch = 32;
++ }
++ if (sbi->s_mb_prefetch >= ext4_get_groups_count(sb))
++ sbi->s_mb_prefetch = ext4_get_groups_count(sb);
++ /* now many real IOs to prefetch within a single allocation at cr=0
++ * given cr=0 is an CPU-related optimization we shouldn't try to
++ * load too many groups, at some point we should start to use what
++ * we've got in memory.
++ * with an average random access time 5ms, it'd take a second to get
++ * 200 groups (* N with flex_bg), so let's make this limit 4 */
++ sbi->s_mb_prefetch_limit = sbi->s_mb_prefetch * 4;
++ if (sbi->s_mb_prefetch_limit > ext4_get_groups_count(sb))
++ sbi->s_mb_prefetch_limit = ext4_get_groups_count(sb);
+
+ sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
+ if (sbi->s_locality_groups == NULL) {
+--- linux-4.18/fs/ext4/mballoc.h 2019-11-28 14:55:26.471545362 +0300
++++ linux-4.18/fs/ext4/mballoc.h 2019-12-02 11:21:57.028104886 +0300
+@@ -177,6 +177,8 @@ struct ext4_allocation_context {
+ struct page *ac_buddy_page;
+ struct ext4_prealloc_space *ac_pa;
+ struct ext4_locality_group *ac_lg;
++ ext4_group_t ac_prefetch;
++ int ac_prefetch_ios; /* number of initialied prefetch IO */
+ };
+
+ #define AC_STATUS_CONTINUE 1
+--- linux-4.18/fs/ext4/super.c 2019-11-28 14:55:26.502545959 +0300
++++ linux-4.18/fs/ext4/super.c 2019-11-28 20:07:48.104558177 +0300
+@@ -190,6 +190,8 @@ EXT4_RW_ATTR_SBI_UI(msg_ratelimit_bur
+ EXT4_RW_ATTR_SBI_UI(mb_small_req, s_mb_small_req);
+ EXT4_RW_ATTR_SBI_UI(mb_large_req, s_mb_large_req);
+ EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
++EXT4_RW_ATTR_SBI_UI(mb_prefetch, s_mb_prefetch);
++EXT4_RW_ATTR_SBI_UI(mb_prefetch_limit, s_mb_prefetch_limit);
+ EXT4_DEPRECATED_ATTR(max_writeback_mb_bump, 128);
+ EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
+ EXT4_ATTR(trigger_fs_error, 0200, NULL, trigger_test_error);
+@@ -223,6 +224,8 @@ static struct attribute *ext4_attrs[]
+ ATTR_LIST(errors_count),
+ ATTR_LIST(first_error_time),
+ ATTR_LIST(last_error_time),
++ ATTR_LIST(mb_prefetch),
++ ATTR_LIST(mb_prefetch_limit),
+ NULL,
+ };
+
--- /dev/null
+--- linux-4.18/fs/ext4/balloc.c 2019-11-28 14:55:26.506546036 +0300
++++ linux-4.18/fs/ext4/balloc.c 2019-12-02 11:21:50.565975537 +0300
+@@ -404,7 +404,8 @@ verified:
+ * Return buffer_head on success or NULL in case of failure.
+ */
+ struct buffer_head *
+-ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
++ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group,
++ int ignore_locked)
+ {
+ struct ext4_group_desc *desc;
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+@@ -435,6 +436,13 @@ ext4_read_block_bitmap_nowait(struct
+ if (bitmap_uptodate(bh))
+ goto verify;
+
++ if (ignore_locked && buffer_locked(bh)) {
++ /* buffer under IO already, do not wait
++ * if called for prefetching */
++ put_bh(bh);
++ return NULL;
++ }
++
+ lock_buffer(bh);
+ if (bitmap_uptodate(bh)) {
+ unlock_buffer(bh);
+@@ -524,7 +532,7 @@ ext4_read_block_bitmap(struct super_b
+ struct buffer_head *bh;
+ int err;
+
+- bh = ext4_read_block_bitmap_nowait(sb, block_group);
++ bh = ext4_read_block_bitmap_nowait(sb, block_group, 0);
+ if (IS_ERR(bh))
+ return bh;
+ err = ext4_wait_block_bitmap(sb, block_group, bh);
+--- linux-4.18/fs/ext4/ext4.h 2019-11-28 14:55:26.470545343 +0300
++++ linux-4.18/fs/ext4/ext4.h 2019-12-02 11:21:40.795779972 +0300
+@@ -1446,6 +1446,8 @@ struct ext4_sb_info {
+ /* where last allocation was done - for stream allocation */
+ unsigned long s_mb_last_group;
+ unsigned long s_mb_last_start;
++ unsigned int s_mb_prefetch;
++ unsigned int s_mb_prefetch_limit;
+
+ /* stats for buddy allocator */
+ atomic_t s_bal_reqs; /* number of reqs with len > 1 */
+@@ -2401,7 +2403,8 @@ extern struct ext4_group_desc * ldisk
+ extern int ext4_should_retry_alloc(struct super_block *sb, int *retries);
+
+ extern struct buffer_head *ext4_read_block_bitmap_nowait(struct super_block *sb,
+- ext4_group_t block_group);
++ ext4_group_t block_group,
++ int ignore_locked);
+ extern int ext4_wait_block_bitmap(struct super_block *sb,
+ ext4_group_t block_group,
+ struct buffer_head *bh);
+--- linux-4.18/fs/ext4/mballoc.c 2019-11-28 14:55:26.500545920 +0300
++++ linux-4.18/fs/ext4/mballoc.c 2019-12-02 11:21:46.656897291 +0300
+@@ -868,7 +868,7 @@ static int ext4_mb_init_cache(struct
+ bh[i] = NULL;
+ continue;
+ }
+- bh[i] = ext4_read_block_bitmap_nowait(sb, group);
++ bh[i] = ext4_read_block_bitmap_nowait(sb, group, 0);
+ if (IS_ERR(bh[i])) {
+ err = PTR_ERR(bh[i]);
+ bh[i] = NULL;
+@@ -2104,6 +2112,87 @@ static int ext4_mb_good_group(struct
+ return 0;
+ }
+
++/*
++ * each allocation context (i.e. a thread doing allocation) has own
++ * sliding prefetch window of @s_mb_prefetch size which starts at the
++ * very first goal and moves ahead of scaning.
++ * a side effect is that subsequent allocations will likely find
++ * the bitmaps in cache or at least in-flight.
++ */
++static void
++ext4_mb_prefetch(struct ext4_allocation_context *ac,
++ ext4_group_t start)
++{
++ struct super_block *sb = ac->ac_sb;
++ ext4_group_t ngroups = ext4_get_groups_count(sb);
++ struct ext4_sb_info *sbi = EXT4_SB(sb);
++ struct ext4_group_info *grp;
++ ext4_group_t group = start;
++ struct buffer_head *bh;
++ int nr;
++
++ /* limit prefetching at cr=0, otherwise mballoc can
++ * spend a lot of time loading imperfect groups */
++ if (ac->ac_criteria < 2 && ac->ac_prefetch_ios >= sbi->s_mb_prefetch_limit)
++ return;
++
++ /* batch prefetching to get few READs in flight */
++ nr = ac->ac_prefetch - group;
++ if (ac->ac_prefetch < group)
++ /* wrapped to the first groups */
++ nr += ngroups;
++ if (nr > 0)
++ return;
++ BUG_ON(nr < 0);
++
++ nr = sbi->s_mb_prefetch;
++ if (ext4_has_feature_flex_bg(sb)) {
++ /* align to flex_bg to get more bitmas with a single IO */
++ nr = (group / sbi->s_mb_prefetch) * sbi->s_mb_prefetch;
++ nr = nr + sbi->s_mb_prefetch - group;
++ }
++ while (nr-- > 0) {
++ grp = ext4_get_group_info(sb, group);
++ /* ignore empty groups - those will be skipped
++ * during the scanning as well */
++ if (grp->bb_free > 0 && EXT4_MB_GRP_NEED_INIT(grp)) {
++ bh = ext4_read_block_bitmap_nowait(sb, group, 1);
++ if (bh && !IS_ERR(bh)) {
++ if (!buffer_uptodate(bh))
++ ac->ac_prefetch_ios++;
++ brelse(bh);
++ }
++ }
++ if (++group >= ngroups)
++ group = 0;
++ }
++ ac->ac_prefetch = group;
++}
++
++static void
++ext4_mb_prefetch_fini(struct ext4_allocation_context *ac)
++{
++ struct ext4_group_info *grp;
++ ext4_group_t group;
++ int nr, rc;
++
++ /* initialize last window of prefetched groups */
++ nr = ac->ac_prefetch_ios;
++ if (nr > EXT4_SB(ac->ac_sb)->s_mb_prefetch)
++ nr = EXT4_SB(ac->ac_sb)->s_mb_prefetch;
++ group = ac->ac_prefetch;
++ while (nr-- > 0) {
++ grp = ext4_get_group_info(ac->ac_sb, group);
++ if (grp->bb_free > 0 && EXT4_MB_GRP_NEED_INIT(grp)) {
++ rc = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS);
++ if (rc)
++ break;
++ }
++ if (group-- == 0)
++ group = ext4_get_groups_count(ac->ac_sb) - 1;
++ }
++}
++
+ static noinline_for_stack int
+ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
+ {
+@@ -2176,6 +2264,7 @@ repeat:
+ * from the goal value specified
+ */
+ group = ac->ac_g_ex.fe_group;
++ ac->ac_prefetch = group;
+
+ for (i = 0; i < ngroups; group++, i++) {
+ int ret = 0;
+@@ -2188,6 +2277,8 @@ repeat:
+ if (group >= ngroups)
+ group = 0;
+
++ ext4_mb_prefetch(ac, group);
++
+ /* This now checks without needing the buddy page */
+ ret = ext4_mb_good_group(ac, group, cr);
+ if (ret <= 0) {
+@@ -2260,6 +2351,8 @@ repeat:
+ out:
+ if (!err && ac->ac_status != AC_STATUS_FOUND && first_err)
+ err = first_err;
++ /* use prefetched bitmaps to init buddy so that read info is not lost */
++ ext4_mb_prefetch_fini(ac);
+ return err;
+ }
+
+@@ -2832,6 +2925,24 @@ int ext4_mb_init(struct super_block *
+ sbi->s_mb_large_req = sbi->s_stripe * 8;
+ sbi->s_mb_group_prealloc = sbi->s_stripe * 4;
+ }
++ if (ext4_has_feature_flex_bg(sb)) {
++ /* a single flex group is supposed to be read by a single IO */
++ sbi->s_mb_prefetch = 1 << sbi->s_es->s_log_groups_per_flex;
++ sbi->s_mb_prefetch *= 8; /* 8 prefetch IOs in flight at most */
++ } else {
++ sbi->s_mb_prefetch = 32;
++ }
++ if (sbi->s_mb_prefetch > ext4_get_groups_count(sb))
++ sbi->s_mb_prefetch = ext4_get_groups_count(sb);
++ /* now many real IOs to prefetch within a single allocation at cr=0
++ * given cr=0 is an CPU-related optimization we shouldn't try to
++ * load too many groups, at some point we should start to use what
++ * we've got in memory.
++ * with an average random access time 5ms, it'd take a second to get
++ * 200 groups (* N with flex_bg), so let's make this limit 4 */
++ sbi->s_mb_prefetch_limit = sbi->s_mb_prefetch * 4;
++ if (sbi->s_mb_prefetch_limit > ext4_get_groups_count(sb))
++ sbi->s_mb_prefetch_limit = ext4_get_groups_count(sb);
+
+ sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
+ if (sbi->s_locality_groups == NULL) {
+--- linux-4.18/fs/ext4/mballoc.h 2019-11-28 14:55:26.471545362 +0300
++++ linux-4.18/fs/ext4/mballoc.h 2019-12-02 11:21:57.028104886 +0300
+@@ -177,6 +177,8 @@ struct ext4_allocation_context {
+ struct page *ac_buddy_page;
+ struct ext4_prealloc_space *ac_pa;
+ struct ext4_locality_group *ac_lg;
++ ext4_group_t ac_prefetch;
++ int ac_prefetch_ios; /* number of initialied prefetch IO */
+ };
+
+ #define AC_STATUS_CONTINUE 1
+--- linux-4.18/fs/ext4/sysfs.c 2019-11-28 14:55:26.502545959 +0300
++++ linux-4.18/fs/ext4/sysfs.c 2019-11-28 20:07:48.104558177 +0300
+@@ -190,6 +190,8 @@ EXT4_RW_ATTR_SBI_UI(msg_ratelimit_bur
+ EXT4_RO_ATTR_ES_UI(errors_count, s_error_count);
+ EXT4_RO_ATTR_ES_UI(first_error_time, s_first_error_time);
+ EXT4_RO_ATTR_ES_UI(last_error_time, s_last_error_time);
++EXT4_RW_ATTR_SBI_UI(mb_prefetch, s_mb_prefetch);
++EXT4_RW_ATTR_SBI_UI(mb_prefetch_limit, s_mb_prefetch_limit);
+
+ static unsigned int old_bump_val = 128;
+ EXT4_ATTR_PTR(max_writeback_mb_bump, 0444, pointer_ui, &old_bump_val);
+@@ -223,6 +224,8 @@ static struct attribute *ext4_attrs[]
+ ATTR_LIST(errors_count),
+ ATTR_LIST(first_error_time),
+ ATTR_LIST(last_error_time),
++ ATTR_LIST(mb_prefetch),
++ ATTR_LIST(mb_prefetch_limit),
+ NULL,
+ };
+
rhel7/ext4-include-terminating-u32-in-size-of-xattr-entries-when-expanding-inodes.patch
rhel7/ext4-optimize-ext4_find_delalloc_range-in-nodelalloc.patch
rhel7/ext4-mballoc-skip-uninit-groups-cr0.patch
+rhel7/ext4-mballoc-prefetch.patch
rhel7/ext4-include-terminating-u32-in-size-of-xattr-entries-when-expanding-inodes.patch
rhel7/ext4-optimize-ext4_find_delalloc_range-in-nodelalloc.patch
rhel7/ext4-mballoc-skip-uninit-groups-cr0.patch
+rhel7/ext4-mballoc-prefetch.patch
rhel7/ext4-include-terminating-u32-in-size-of-xattr-entries-when-expanding-inodes.patch
rhel7/ext4-optimize-ext4_find_delalloc_range-in-nodelalloc.patch
rhel7/ext4-mballoc-skip-uninit-groups-cr0.patch
+rhel7/ext4-mballoc-prefetch.patch
rhel7.2/ext4-export-mb-stream-allocator-variables.patch
rhel7/ext4-optimize-ext4_find_delalloc_range-in-nodelalloc.patch
rhel7/ext4-mballoc-skip-uninit-groups-cr0.patch
+rhel7/ext4-mballoc-prefetch.patch
rhel7/ext4-optimize-ext4_find_delalloc_range-in-nodelalloc.patch
rhel7.2/ext4-simple-blockalloc.patch
rhel7/ext4-mballoc-skip-uninit-groups-cr0.patch
+rhel7/ext4-mballoc-prefetch.patch
rhel7.7/ext4-fix-project-with-unpatched-kernel.patch
rhel7.2/ext4-simple-blockalloc.patch
rhel7/ext4-mballoc-skip-uninit-groups-cr0.patch
+rhel7.7/ext4-mballoc-prefetch.patch
rhel7/ext4-include-terminating-u32-in-size-of-xattr-entries-when-expanding-inodes.patch
rhel7/ext4-optimize-ext4_find_delalloc_range-in-nodelalloc.patch
rhel7/ext4-mballoc-skip-uninit-groups-cr0.patch
+rhel7/ext4-mballoc-prefetch.patch
rhel8/ext4-export-mb-stream-allocator-variables.patch
rhel8/ext4-simple-blockalloc.patch
rhel8/ext4-mballoc-skip-uninit-groups-cr0.patch
+rhel8/ext4-mballoc-prefetch.patch
git://git.whamcloud.com / fs / lustre-release.git / commitdiff