Messages in this thread | | | Date | Mon, 7 Sep 2009 16:15:48 +0200 | From | Nick Piggin <> | Subject | Re: [RFC][PATCH] mm: write_cache_pages be more sequential |
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On Mon, Sep 07, 2009 at 05:07:38PM +0300, Adrian Hunter wrote: > >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.
Why does page 2 get set dirty if the write was incomplete?
> 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;
Doesn't this just break range_cyclic? range_cyclic is supposed to work across calls to write_cache_pages, and it's there I guess so background writeout will be able to eventually get around to writing all pages relatively fairly in the presence of redirtying operations.
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