[PATCH] fadvise: only initiate writeback for specified range with FADV_DONTNEED

[Shawn Bohrer]

Previously POSIX_FADV_DONTNEED would start writeback for the entire file
when the bdi was not write congested.  This negatively impacts
performance if the file contians dirty pages outside of the requested
range.  This change uses __filemap_fdatawrite_range() to only initiate
writeback for the requested range.

Signed-off-by: Shawn Bohrer <sbohrer@xxxxxxxxxxxxxxx>
---
 mm/fadvise.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/mm/fadvise.c b/mm/fadvise.c
index 8d723c9..469491e 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -117,7 +117,8 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
 		break;
 	case POSIX_FADV_DONTNEED:
 		if (!bdi_write_congested(mapping->backing_dev_info))
-			filemap_flush(mapping);
+			__filemap_fdatawrite_range(mapping, offset, endbyte,
+						   WB_SYNC_NONE);
 
 		/* First and last FULL page! */
 		start_index = (offset+(PAGE_CACHE_SIZE-1)) >> PAGE_CACHE_SHIFT;
-- 
1.7.6



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