Messages in this thread | | | Date | Thu, 21 Apr 2011 18:41:54 +0200 | From | Jan Kara <> | Subject | Re: [PATCH 5/6] writeback: try more writeback as long as something was written |
| |
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...
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...
Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR
| |