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From: David Sterba <dsterba@suse.cz>
To: Josef Bacik <josef@toxicpanda.com>
Cc: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH 0/2] Drop some mis-uses of READA
Date: Wed, 18 Mar 2020 15:40:49 +0100	[thread overview]
Message-ID: <20200318144049.GY12659@twin.jikos.cz> (raw)
In-Reply-To: <20200313210954.148686-1-josef@toxicpanda.com>

On Fri, Mar 13, 2020 at 05:09:52PM -0400, Josef Bacik wrote:
> In debugging Zygo's huge commit delays I noticed we were burning a bunch of time
> doing READA in cases where we don't need to.  The way READA works in btrfs is
> we'll load up adjacent nodes and leaves as we walk down.  This is useful for
> operations where we're going to be reading sequentially across the tree.
> 
> But for delayed refs we're looking up one bytenr, and then another one which
> could be elsewhere in the tree.  With large enough extent trees this results in
> a lot of unneeded latency.
> 
> The same applies to build_backref_tree, but that's even worse because we're
> looking up backrefs, which are essentially randomly spread out across the extent
> root.  Thanks,

Makes sense, I'll add it to misc-next. Thanks.

      parent reply	other threads:[~2020-03-18 14:41 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-13 21:09 [PATCH 0/2] Drop some mis-uses of READA Josef Bacik
2020-03-13 21:09 ` [PATCH 1/2] btrfs: do not use READA for running delayed refs Josef Bacik
2020-03-14  0:18   ` Qu Wenruo
2020-03-13 21:09 ` [PATCH 2/2] btrfs: do not READA in build_backref_tree Josef Bacik
2020-03-14  0:19   ` Qu Wenruo
2020-03-14  2:56 ` [PATCH 0/2] Drop some mis-uses of READA Qu Wenruo
2020-03-18 14:44   ` David Sterba
2020-03-18 14:40 ` David Sterba [this message]

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