Messages in this thread | | | Date | Thu, 29 Apr 2004 08:19:42 -0500 (CDT) | From | Brent Cook <> | Subject | Re: pdflush eating a lot of CPU on heavy NFS I/O |
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On Wed, 28 Apr 2004, Andrew Morton wrote:
> Brent Cook <busterbcook@yahoo.com> wrote: > > > > On Wed, 28 Apr 2004, Andrew Morton wrote: > > > > > Brent Cook <busterbcook@yahoo.com> wrote: > > > > > > > > sync_sb_inodes: write inode c55d25bc > > > > __sync_single_inode: writepages in nr_pages:25 nr_to_write:949 > > > > pages_skipped:0 en:0 > > > > __sync_single_inode: writepages in nr_pages:25 nr_to_write:949 > > > > pages_skipped:0 en:0 > > > > > > uh-huh. > > > > > > Does this fix it? > > > > I'm going to run a compile/load test overnight, but the test that > > triggered it every time previously failed to do so with this patch. > > OK, thanks. A better patch would be:
No, thank you! The overnight test was successful. I have been running this better patch for a little while, and it is no worse. I think you have solved the bigger problem, which was the runaway process, at least for me.
So, moving it to the tail of the s_dirty list now puts that page in a higher-priority to be written back next time? That sounds better than just redirtying it; the poor inode has been through enough as it is without having to wait even longer.
If you want to think about it a little more, pdflush on 2.6.6-rc3 with this patch still seems to use more resources than it did on 2.6.5. With heavy NFS traffic, it still uses about 2-3% CPU on 2.6.6-rc3, but on 2.6.5 it averages about 0.1%. Maybe it just wasn't being used to its full potential in 2.6.5?
Thanks - Brent
> > diff -puN fs/fs-writeback.c~writeback-livelock-fix-2 fs/fs-writeback.c > --- 25/fs/fs-writeback.c~writeback-livelock-fix-2 2004-04-28 21:19:32.779061976 -0700 > +++ 25-akpm/fs/fs-writeback.c 2004-04-28 21:20:11.080239312 -0700 > @@ -176,11 +176,12 @@ __sync_single_inode(struct inode *inode, > if (wbc->for_kupdate) { > /* > * For the kupdate function we leave the inode > - * where it is on sb_dirty so it will get more > + * at the head of sb_dirty so it will get more > * writeout as soon as the queue becomes > * uncongested. > */ > inode->i_state |= I_DIRTY_PAGES; > + list_move_tail(&inode->i_list, &sb->s_dirty); > } else { > /* > * Otherwise fully redirty the inode so that > > _ > > > pdflush is behaving so far, and I'll say you've figured it out for now, > > with the final verdict in about 8 hours. > > > > Does this mean that, if there were too many dirty pages and not enough > > time to write them all back, that the dirty page list just stopped being > > traversed, stuck on a single page? > > No.. There's all sorts of livelock avoidance code in there and I keep on > forgetting that sometimes writepage won't write the dang page at all - > instead it just redirties the page (and hence the inode). > > Now, that redirtying of the inode _should_ have moved the inode off the > s_io list and onto the s_dirty list. But for some reason it looks like it > didn't, so we get stuck in a loop. I need to think about it a bit more. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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