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From: "Theodore Ts'o" <tytso@mit.edu>
To: Dominique MARTINET <dominique.martinet@atmark-techno.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
	linux-btrfs@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	Yu Kuai <yukuai3@huawei.com>,
	Kent Overstreet <kent.overstreet@gmail.com>
Subject: Re: Major btrfs fiemap slowdown on file with many extents once in cache (RCU stalls?) (Was: [PATCH 1/3] filemap: Correct the conditions for marking a folio as accessed)
Date: Thu, 30 Jun 2022 10:37:58 -0400	[thread overview]
Message-ID: <Yr21RoL+ztf1W5Od@mit.edu> (raw)
In-Reply-To: <Yr1QwVW+sHWlAqKj@atmark-techno.com>

On Thu, Jun 30, 2022 at 04:29:05PM +0900, Dominique MARTINET wrote:
> Hi Willy, linux-btrfs@vger,
> 
> Matthew Wilcox (Oracle) wrote on Sun, Jun 19, 2022 at 04:11:41PM +0100:
> > We had an off-by-one error which meant that we never marked the first page
> > in a read as accessed.  This was visible as a slowdown when re-reading
> > a file as pages were being evicted from cache too soon.  In reviewing
> > this code, we noticed a second bug where a multi-page folio would be
> > marked as accessed multiple times when doing reads that were less than
> > the size of the folio.
> 
> when debugging an unrelated issue (short reads on btrfs with io_uring
> and O_DIRECT[1]), I noticed that my horrible big file copy speeds fell
> down from ~2GB/s (there's compression and lots of zeroes) to ~100MB/s
> the second time I was copying it with cp.
> 
> I've taken a moment to bisect this and came down to this patch.

I think you may have forgotten to include the commit-id that was the
results of your bisect.... ?

					- Ted

  reply	other threads:[~2022-06-30 14:39 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20220619151143.1054746-1-willy@infradead.org>
     [not found] ` <20220619151143.1054746-2-willy@infradead.org>
2022-06-30  7:29   ` Major btrfs fiemap slowdown on file with many extents once in cache (RCU stalls?) (Was: [PATCH 1/3] filemap: Correct the conditions for marking a folio as accessed) Dominique MARTINET
2022-06-30 14:37     ` Theodore Ts'o [this message]
2022-06-30 22:43       ` Dominique MARTINET
2022-07-01  1:55     ` Yu Kuai
2022-07-07  8:42       ` Dominique MARTINET

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