Messages in this thread Patch in this message | | | Date | Wed, 23 Sep 2009 09:27:00 +0800 | From | Wu Fengguang <> | Subject | Re: regression in page writeback |
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On Wed, Sep 23, 2009 at 09:17:58AM +0800, Wu Fengguang wrote: > On Wed, Sep 23, 2009 at 08:54:52AM +0800, Andrew Morton wrote: > > On Wed, 23 Sep 2009 08:22:20 +0800 Wu Fengguang <fengguang.wu@intel.com> wrote: > > > > > Jens' per-bdi writeback has another improvement. In 2.6.31, when > > > superblocks A and B both have 100000 dirty pages, it will first > > > exhaust A's 100000 dirty pages before going on to sync B's. > > > > That would only be true if someone broke 2.6.31. Did they? > > > > SYSCALL_DEFINE0(sync) > > { > > wakeup_pdflush(0); > > sync_filesystems(0); > > sync_filesystems(1); > > if (unlikely(laptop_mode)) > > laptop_sync_completion(); > > return 0; > > } > > > > the sync_filesystems(0) is supposed to non-blockingly start IO against > > all devices. It used to do that correctly. But people mucked with it > > so perhaps it no longer does. > > I'm referring to writeback_inodes(). Each invocation of which (to sync > 4MB) will do the same iteration over superblocks A => B => C ... So if > A has dirty pages, it will always be served first. > > So if wbc->bdi == NULL (which is true for kupdate/background sync), it > will have to first exhaust A before going on to B and C. > > There are no "cursor" in the superblock level iterations.
I even have an old patch for it. But Jens' patches are more general solution.
Thanks, Fengguang --- writeback: continue from the last super_block in syncing
Cc: David Chinner <dgc@sgi.com> Cc: Michael Rubin <mrubin@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> --- fs/fs-writeback.c | 12 ++++++++++++ include/linux/writeback.h | 2 ++ 2 files changed, 14 insertions(+)
--- linux-2.6.orig/fs/fs-writeback.c +++ linux-2.6/fs/fs-writeback.c @@ -494,11 +494,19 @@ void writeback_inodes(struct writeback_control *wbc) { struct super_block *sb; + int i; + + if (wbc->sb_index) + wbc->more_io = 1; might_sleep(); spin_lock(&sb_lock); restart: + i = -1; list_for_each_entry_reverse(sb, &super_blocks, s_list) { + i++; + if (i < wbc->sb_index) + continue; if (sb_has_dirty_inodes(sb)) { /* we're making our own get_super here */ sb->s_count++; @@ -520,9 +528,13 @@ restart: if (__put_super_and_need_restart(sb)) goto restart; } + if (list_empty(&sb->s_io)) + wbc->sb_index++; if (wbc->nr_to_write <= 0) break; } + if (&sb->s_list == &super_blocks) + wbc->sb_index = 0; spin_unlock(&sb_lock); } --- linux-2.6.orig/include/linux/writeback.h +++ linux-2.6/include/linux/writeback.h @@ -48,6 +48,8 @@ struct writeback_control { this for each page written */ long pages_skipped; /* Pages which were not written */ + int sb_index; /* the superblock to continue from */ + /* * For a_ops->writepages(): is start or end are non-zero then this is * a hint that the filesystem need only write out the pages inside that
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