Re: [LKP] [lkp] [xfs] 68a9f5e700: aim7.jobs-per-min -13.6% regression

Christoph Hellwig
2016-08-11T20:00:23Z

On Thu, Aug 11, 2016 at 12:51:31PM -0700, Linus Torvalds wrote:
> Ok. It does seem to also reset the active file page counts back, so
> that part did seem to be related, but yeah, from a performance
> standpoint that was clearly not a major issue.
>
> Let's hope Dave can figure out something based on his numbers, because
> I'm out of ideas. Or maybe it's the pagefault-atomic thing that
> Christoph was looking at.

I can't really think of any reason why the pagefaul_disable() would
sіgnificantly change performance. Anyway, the patch for the is below
(on top of the previous mark_page_accessed() one), so feel free to
re-run the test with it. It would also be nice to see the profiles
with the two patches applied.

commit 43106eea246074acc4bb7d12fdb91f58002f52ed
Author: Christoph Hellwig <hch@lst.de>
Date: Thu Aug 11 10:41:40 2016 -0700

fs: remove superflous pagefault_disable from iomap_write_actor

No idea where this really came from, generic_perform_write only briefly
did a pagefaul_disable when trying a different prefault scheme.

Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/iomap.c b/fs/iomap.c
index f39c318..74712e2 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -194,9 +194,7 @@ again:
if (mapping_writably_mapped(inode->i_mapping))
flush_dcache_page(page);

- pagefault_disable();
copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
- pagefault_enable();

flush_dcache_page(page);