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authorFengguang Wu <wfg@mail.ustc.edu.cn>2007-10-17 02:30:43 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-17 11:43:02 -0400
commit2e6883bdf49abd0e7f0d9b6297fc3be7ebb2250b (patch)
treeaec0418150413c7e9f43fb2ec68bfd24738b0623 /include/linux/writeback.h
parent1f7decf6d9f06dac008b8d66935c0c3b18e564f9 (diff)
writeback: introduce writeback_control.more_io to indicate more io
After making dirty a 100M file, the normal behavior is to start the writeback for all data after 30s delays. But sometimes the following happens instead: - after 30s: ~4M - after 5s: ~4M - after 5s: all remaining 92M Some analyze shows that the internal io dispatch queues goes like this: s_io s_more_io ------------------------- 1) 100M,1K 0 2) 1K 96M 3) 0 96M 1) initial state with a 100M file and a 1K file 2) 4M written, nr_to_write <= 0, so write more 3) 1K written, nr_to_write > 0, no more writes(BUG) nr_to_write > 0 in (3) fools the upper layer to think that data have all been written out. The big dirty file is actually still sitting in s_more_io. We cannot simply splice s_more_io back to s_io as soon as s_io becomes empty, and let the loop in generic_sync_sb_inodes() continue: this may starve newly expired inodes in s_dirty. It is also not an option to draw inodes from both s_more_io and s_dirty, an let the loop go on: this might lead to live locks, and might also starve other superblocks in sync time(well kupdate may still starve some superblocks, that's another bug). We have to return when a full scan of s_io completes. So nr_to_write > 0 does not necessarily mean that "all data are written". This patch introduces a flag writeback_control.more_io to indicate this situation. With it the big dirty file no longer has to wait for the next kupdate invocation 5s later. Cc: David Chinner <dgc@sgi.com> Cc: Ken Chen <kenchen@google.com> Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/writeback.h')
-rw-r--r--include/linux/writeback.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 52be879793ed..1200868a5dee 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -62,6 +62,7 @@ struct writeback_control {
62 unsigned for_reclaim:1; /* Invoked from the page allocator */ 62 unsigned for_reclaim:1; /* Invoked from the page allocator */
63 unsigned for_writepages:1; /* This is a writepages() call */ 63 unsigned for_writepages:1; /* This is a writepages() call */
64 unsigned range_cyclic:1; /* range_start is cyclic */ 64 unsigned range_cyclic:1; /* range_start is cyclic */
65 unsigned more_io:1; /* more io to be dispatched */
65}; 66};
66 67
67/* 68/*