From: Nikolay Borisov <nborisov@suse.com>
To: Qu Wenruo <wqu@suse.com>, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 1/3] btrfs: file-item: use nodesize to determine whether we need readhead for btrfs_lookup_bio_sums()
Date: Thu, 29 Oct 2020 09:25:33 +0200 [thread overview]
Message-ID: <d1f78e95-9759-f2dc-23b9-2690dac6cfb5@suse.com> (raw)
In-Reply-To: <20201028072432.86907-2-wqu@suse.com>
On 28.10.20 г. 9:24 ч., Qu Wenruo wrote:
> In btrfs_lookup_bio_sums() if the bio is pretty large, we want to
> readahead the csum tree.
>
> However the threshold is an immediate number, (PAGE_SIZE * 8), from the
> initial btrfs merge.
>
> The value itself is pretty hard to guess the meaning, especially when
> the immediate number is from the age where 4K sectorsize is the default
> and only CRC32 is supported.
>
> For the most common btrfs setup, CRC32 csum algorithme 4K sectorsize,
> it means just 32K read would kick readahead, while the csum itself is
> only 32 bytes in size.
>
> Now let's be more reasonable by taking both csum size and node size into
> consideration.
>
> If the csum size for the bio is larger than one node, then we kick the
> readahead.
> This means for current default btrfs, the threshold will be 16M.
>
> This change should not change performance observably, thus this is mostly
> a readability enhancement.
>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
next prev parent reply other threads:[~2020-10-29 7:26 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-28 7:24 [PATCH 0/3] btrfs: btrfs_lookup_bio_sums() related fixes Qu Wenruo
2020-10-28 7:24 ` [PATCH 1/3] btrfs: file-item: use nodesize to determine whether we need readhead for btrfs_lookup_bio_sums() Qu Wenruo
2020-10-29 7:25 ` Nikolay Borisov [this message]
2020-10-28 7:24 ` [PATCH 2/3] btrfs: ordered-data: rename parameter @len to @nr_sectors Qu Wenruo
2020-10-29 7:32 ` Nikolay Borisov
2020-11-03 19:16 ` David Sterba
2020-11-03 19:23 ` Amy Parker
2020-11-03 23:36 ` Qu Wenruo
2020-10-28 7:24 ` [PATCH 3/3] btrfs: file-item: refactor btrfs_lookup_bio_sums() to handle out-of-order bvecs Qu Wenruo
2020-11-03 19:46 ` David Sterba
2020-11-03 23:42 ` Qu Wenruo
2020-11-16 16:27 ` David Sterba
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