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From: Kent Overstreet <kent.overstreet@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
	viro@zeniv.linux.org.uk, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 2/2] fs: generic_file_buffered_read() now uses find_get_pages_contig
Date: Tue, 9 Jun 2020 21:46:29 -0400	[thread overview]
Message-ID: <20200610014629.GB4070152@moria.home.lan> (raw)
In-Reply-To: <20200610013808.GF19604@bombadil.infradead.org>

On Tue, Jun 09, 2020 at 06:38:08PM -0700, Matthew Wilcox wrote:
> On Tue, Jun 09, 2020 at 08:10:36PM -0400, Kent Overstreet wrote:
> > Convert generic_file_buffered_read() to get pages to read from in
> > batches, and then copy data to userspace from many pages at once - in
> > particular, we now don't touch any cachelines that might be contended
> > while we're in the loop to copy data to userspace.
> > 
> > This is is a performance improvement on workloads that do buffered reads
> > with large blocksizes, and a very large performance improvement if that
> > file is also being accessed concurrently by different threads.
> 
> Hey, you're stealing my performance improvements!

:)

> Granted, I haven't got to doing performance optimisations (certainly
> not in this function), but this is one of the places where THP in the
> page cache will have a useful performance improvement.
> 
> I'm not opposed to putting this in, but I may back it out as part of
> the THP work because the THPs will get the same performance improvements
> that you're seeing here with less code.

I'm an _enthusiastic_ supporter of the THP stuff (as you know), but my feeling
is that it's going to be a long time before hugepages are everywhere - and I
think even with the pagevec stuff generic_file_buffered_read() is somewhat
easier to read and deal with after this series than before it.

Though I could see the pagevec stuff making hugepage support a pain, so there is
that. Eh.

  reply	other threads:[~2020-06-10  1:46 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-10  0:10 [PATCH 0/2] generic_file_buffered_read() refactoring & optimization Kent Overstreet
2020-06-10  0:10 ` [PATCH 1/2] fs: Break generic_file_buffered_read up into multiple functions Kent Overstreet
2020-06-10  0:10 ` [PATCH 2/2] fs: generic_file_buffered_read() now uses find_get_pages_contig Kent Overstreet
2020-06-10  0:47   ` Matthew Wilcox
2020-06-10  1:08     ` Kent Overstreet
2020-06-10  1:38   ` Matthew Wilcox
2020-06-10  1:46     ` Kent Overstreet [this message]
2020-06-10  1:36 ` [PATCH v2 1/2] fs: Break generic_file_buffered_read up into multiple functions Kent Overstreet
2020-06-10  1:36 ` [PATCH v2 2/2] fs: generic_file_buffered_read() now uses find_get_pages_contig Kent Overstreet
2020-06-18  1:05   ` Andrew Morton
2020-06-19  3:20     ` [PATCH v3 0/2] generic_file_buffered_read() refactoring & optimization Kent Overstreet
2020-06-19 12:59       ` Christoph Hellwig
2020-06-19 18:44         ` Kent Overstreet
2020-06-19  3:20     ` [PATCH v3 1/2] fs: Break generic_file_buffered_read up into multiple functions Kent Overstreet
2020-06-19  3:20     ` [PATCH v3 2/2] fs: generic_file_buffered_read() now uses find_get_pages_contig Kent Overstreet
2020-06-30  0:12 ` Fixup patch for [PATCH 0/2] generic_file_buffered_read() refactoring & optimization Kent Overstreet
  -- strict thread matches above, loose matches on Subject: below --
2020-10-17 20:10 [PATCH 0/2] generic_file_buffered_read() refactoring, perf improvements Kent Overstreet
2020-10-17 20:10 ` [PATCH 2/2] fs: generic_file_buffered_read() now uses find_get_pages_contig Kent Overstreet
2020-10-20 14:47   ` Jens Axboe
2018-08-15 23:26 [PATCH 0/2] generic_file_buffered_read improvements Kent Overstreet
2018-08-15 23:26 ` [PATCH 2/2] fs: generic_file_buffered_read() now uses find_get_pages_contig Kent Overstreet
2018-08-16 14:56   ` kbuild test robot

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