Messages in this thread Patch in this message | | | Date | Mon, 07 Sep 2009 17:07:38 +0300 | From | Adrian Hunter <> | Subject | [RFC][PATCH] mm: write_cache_pages be more sequential |
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From 6f3bb7c26936c45d810048f59c369e8d5a5623fc Mon Sep 17 00:00:00 2001 From: Adrian Hunter <adrian.hunter@nokia.com> Date: Mon, 7 Sep 2009 10:49:11 +0300 Subject: [PATCH] mm: write_cache_pages be more sequential
If a file is written to sequentially, then writeback should write the pages sequentially also. However, that does not always happen. For example:
1) user writes pages 0, 1 and 2 but 2 is incomplete 2) write_cache_pages writes pages 0, 1 and 2 and sets writeback_index to 3 3) user finishes writing page 2 and writes pages 3 and 4 4) write_cache_pages writes pages 3 and 4, and then cycles back and writes page 2 again.
So the pages are written out in the order 0, 1, 2, 3 ,4 ,2 instead of 0, 1, 2, 2, 3, 4.
This situation was noticed on UBIFS because it writes directly from writepage. Hence if there is an unexpected power-loss, a file will end up with a hole even though the file was written sequentially by the user.
Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com> --- mm/page-writeback.c | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 81627eb..7410b7a 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -960,6 +960,8 @@ int write_cache_pages(struct address_space *mapping, pagevec_init(&pvec, 0); if (wbc->range_cyclic) { writeback_index = mapping->writeback_index; /* prev offset */ + if (writeback_index) + writeback_index -= 1; index = writeback_index; if (index == 0) cycled = 1; -- 1.5.6.3
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