On Fri, Apr 22, 2011 at 12:41:54AM +0800, Jan Kara wrote: > On Thu 21-04-11 14:05:56, Wu Fengguang wrote: > > On Thu, Apr 21, 2011 at 12:39:40PM +0800, Christoph Hellwig wrote: > > > On Thu, Apr 21, 2011 at 11:33:25AM +0800, Wu Fengguang wrote: > > > > I collected the writeback_single_inode() traces (patch attached for > > > > your reference) each for several test runs, and find much more > > > > I_DIRTY_PAGES after patchset. Dave, do you know why there are so many > > > > I_DIRTY_PAGES (or radix tag) remained after the XFS ->writepages() call, > > > > even for small files? > > > > > > What is your defintion of a small file? As soon as it has multiple > > > extents or holes there's absolutely no way to clean it with a single > > > writepage call. > > > > It's writing a kernel source tree to XFS. You can find in the below > > trace that it often leaves more dirty pages behind (indicated by the > > I_DIRTY_PAGES flag) after writing as less as 1 page (indicated by the > > wrote=1 field). > As Dave said, it's probably just a race since XFS redirties the inode on > IO completion. So I think the inodes are just small so they have only a few > dirty pages so you don't have much to write and they are written and > redirtied before you check the I_DIRTY flags. You could use radix tree > dirty tag to verify whether there are really dirty pages or not... Yeah, Dave and Christoph root caused it in the other email -- XFS sets I_DIRTY which accidentally sets I_DIRTY_PAGES. We can safely bet there are no real dirty pages -- otherwise it would have turned up as performance regressions. > BTW a quick check of kernel tree shows the following distribution of > sizes (in KB): > Count KB Cumulative Percent > 257 0 0.9% > 13309 4 45% > 5553 8 63% > 2997 12 73% > 1879 16 80% > 1275 20 83% > 987 24 87% > 685 28 89% > 540 32 91% > 387 36 ... > 309 40 > 264 44 > 249 48 > 170 52 > 143 56 > 144 60 > 132 64 > 100 68 > ... > Total 30155 > > And the distribution of your 'wrote=xxx' roughly corresponds to this... Nice numbers! How do you manage to account them? :) Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
