From: Matthew Wilcox <willy@infradead.org>
To: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
Cc: ntfs3@lists.linux.dev, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH RFC] fs/ntfs3: disable readahead for compressed files
Date: Sat, 1 Nov 2025 16:01:58 +0000 [thread overview]
Message-ID: <aQYu9jktrEAsx2y0@casper.infradead.org> (raw)
In-Reply-To: <20251028165131.9187-1-almaz.alexandrovich@paragon-software.com>
On Tue, Oct 28, 2025 at 05:51:31PM +0100, Konstantin Komarov wrote:
> Reading large compressed files is extremely slow when readahead is enabled.
> For example, reading a 4 GB XPRESS-4K compressed file (compression ratio
> ≈ 4:1) takes about 230 minutes with readahead enabled, but only around 3
> minutes when readahead is disabled.
>
> The issue was first observed in January 2025 and is reproducible with large
> compressed NTFS files. Disabling readahead for compressed files avoids this
> performance regression, although this may not be the ideal long-term fix.
>
> This patch is submitted as an RFC to gather feedback on whether disabling
> readahead is an acceptable solution or if a more targeted fix should be
> implemented.
I suspect your real problem is that readahead is synchronous in ntfs3
and the VFS is not expecting this. Your get_block (ntfs_get_block_vbo)
calls bh_read() which waits for the I/O to complete. That means we get
no pipelining which will significantly reduce bandwidth.
prev parent reply other threads:[~2025-11-01 16:02 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-28 16:51 Konstantin Komarov
2025-11-01 16:01 ` Matthew Wilcox [this message]
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