From 816042a3a07cd57a27343a4961e85d8f237a11d8 Mon Sep 17 00:00:00 2001
From: jxiong <jxiong>
Date: Fri, 13 Jul 2007 09:11:40 +0000
Subject: [PATCH] r=alex,nathan b=11890

Raid5 write zerocopy support for rhel-2.6 kernels.
---
 lustre/autoconf/lustre-core.m4                | 24 ++++++++++++++++++++++++
 lustre/kernel_patches/series/2.6-rhel4.series |  1 +
 lustre/obdfilter/filter_io_26.c               | 22 ++++++++++++++++++++++
 3 files changed, 47 insertions(+)

diff --git a/lustre/autoconf/lustre-core.m4 b/lustre/autoconf/lustre-core.m4
index 0359013..3d34d0f 100644
--- a/lustre/autoconf/lustre-core.m4
+++ b/lustre/autoconf/lustre-core.m4
@@ -1005,6 +1005,27 @@ LB_LINUX_TRY_COMPILE([
 ])
 ])
 
+#
+# LC_PAGE_CONSTANT
+#
+# In order to support raid5 zerocopy patch, we have to patch the kernel to make
+# it support constant page, which means the page won't be modified during the
+# IO.
+#
+AC_DEFUN([LC_PAGE_CONSTANT],
+[AC_MSG_CHECKING([if kernel have PageConstant defined])
+LB_LINUX_TRY_COMPILE([
+        #include <linux/page-flags.h>
+],[
+        PageConstant((struct page *)NULL);
+],[
+        AC_MSG_RESULT(yes)
+        AC_DEFINE(HAVE_PAGE_CONSTANT, 1, [kernel have PageConstant supported])
+],[
+        AC_MSG_RESULT(no);
+])
+])
+
 # RHEL5 in FS-cache patch rename PG_checked flag
 # into PG_fs_misc
 AC_DEFUN([LC_PG_FS_MISC],
@@ -1106,6 +1127,9 @@ LC_GENERIC_FILE_WRITE
 
 # 2.6.20
 LC_CANCEL_DIRTY_PAGE
+
+# raid5-zerocopy patch
+LC_PAGE_CONSTANT
 ])
 
 #
diff --git a/lustre/kernel_patches/series/2.6-rhel4.series b/lustre/kernel_patches/series/2.6-rhel4.series
index 67ac232..632e352 100644
--- a/lustre/kernel_patches/series/2.6-rhel4.series
+++ b/lustre/kernel_patches/series/2.6-rhel4.series
@@ -22,6 +22,7 @@ raid5-large-io.patch
 raid5-stripe-by-stripe-handling.patch
 raid5-merge-ios.patch
 raid5-serialize-ovelapping-reqs.patch
+raid5-zerocopy.patch
 jbd-stats-2.6.9.patch 
 bitops_ext2_find_next_le_bit-2.6.patch 
 quota-deadlock-on-pagelock-core.patch
diff --git a/lustre/obdfilter/filter_io_26.c b/lustre/obdfilter/filter_io_26.c
index ca43c76..687ae15 100644
--- a/lustre/obdfilter/filter_io_26.c
+++ b/lustre/obdfilter/filter_io_26.c
@@ -104,6 +104,11 @@ static int dio_complete_routine(struct bio *bio, unsigned int done, int error)
         struct filter_iobuf *iobuf = bio->bi_private;
         unsigned long        flags;
 
+#ifdef HAVE_PAGE_CONSTANT
+	struct bio_vec *bvl;
+	int i;
+#endif
+
         /* CAVEAT EMPTOR: possibly in IRQ context 
          * DO NOT record procfs stats here!!! */
 
@@ -128,6 +133,11 @@ static int dio_complete_routine(struct bio *bio, unsigned int done, int error)
                 return 0;
         }
 
+#ifdef HAVE_PAGE_CONSTANT
+	bio_for_each_segment(bvl, bio, i)
+		ClearPageConstant(bvl->bv_page);
+#endif
+
         spin_lock_irqsave(&iobuf->dr_lock, flags);
         if (iobuf->dr_error == 0)
                 iobuf->dr_error = error;
@@ -295,6 +305,18 @@ int filter_do_bio(struct obd_export *exp, struct inode *inode,
                                (blocks[block_idx + i + nblocks] << sector_bits))
                                 nblocks++;
 
+#ifdef HAVE_PAGE_CONSTANT
+			/* I only set the page to be constant only if it 
+		 	 * is mapped to a contiguous underlying disk block(s). 
+			 * It will then make sure the corresponding device 
+			 * cache of raid5 will be overwritten by this page. 
+			 * - jay */
+                        if ((rw == OBD_BRW_WRITE) && 
+                            (nblocks == blocks_per_page) && 
+                            mapping_cap_page_constant_write(inode->i_mapping))
+                               SetPageConstant(page);
+#endif
+
                         if (bio != NULL &&
                             can_be_merged(bio, sector) &&
                             bio_add_page(bio, page,
-- 
1.8.3.1