linux-kernel - Re: [RFC PATCH 1/1] FUSE: Add FUSE_TRUST_MAX_RA flag enabling readahead settings >128KB.

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Message-ID: <CAJfpegvpKKO-dFg7P8fERq5-BcQSC7uh2cYzz-Ufo7wHvnvv9g@mail.gmail.com>
Date:   Thu, 10 Mar 2022 11:27:45 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Kevin Vigor <kvigor@...il.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] FUSE: Add FUSE_TRUST_MAX_RA flag enabling
 readahead settings >128KB.

On Wed, 2 Mar 2022 at 18:18, Kevin Vigor <kvigor@...il.com> wrote:
>
> The existing process_init_reply() in fs/fuse/inode.c sets the ra_pages
> value to the minimum of the max_readahead value provided by the user
> and the pre-existing ra_pages value, which is initialized to
> VM_READAHEAD_PAGES. This makes it impossible to increase the readahead
> value to larger values.
>
> Add a new flag which causes us to blindly accept the user-provided
> value. Note that the existing read_ahead_kb sysfs entry for normal
> block devices does the same (simply accepts user-provided values
> directly with no checks).

read_ahead_kb only allows root to open for write.  Allowing non-root
arbitrary read ahead window size is not a good idea, IMO.

Thanks,
Miklos