linux-kernel - Re: [PATCH] fuse: enable larger read buffers for readdir.

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Message-ID: <831e5a03-7126-3d45-2137-49c1a25769df@spawn.link>
Date:   Wed, 26 Jul 2023 17:23:39 +0000
From:   Antonio SJ Musumeci <trapexit@...wn.link>
To:     Bernd Schubert <bernd.schubert@...tmail.fm>,
        Jaco Kroon <jaco@....co.za>,
        Miklos Szeredi <miklos@...redi.hu>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fuse: enable larger read buffers for readdir.

On 7/26/23 10:45, Bernd Schubert wrote:
>
> On 7/26/23 17:26, Jaco Kroon wrote:
>> Hi,
>>
>> On 2023/07/26 15:53, Bernd Schubert wrote:
>>>
>>> On 7/26/23 12:59, Jaco Kroon wrote:
>>>> Signed-off-by: Jaco Kroon <jaco@....co.za>
>>>> ---
>>>>    fs/fuse/Kconfig   | 16 ++++++++++++++++
>>>>    fs/fuse/readdir.c | 42 ++++++++++++++++++++++++------------------
>>>>    2 files changed, 40 insertions(+), 18 deletions(-)
>>>>
>>>> diff --git a/fs/fuse/Kconfig b/fs/fuse/Kconfig
>>>> index 038ed0b9aaa5..0783f9ee5cd3 100644
>>>> --- a/fs/fuse/Kconfig
>>>> +++ b/fs/fuse/Kconfig
>>>> @@ -18,6 +18,22 @@ config FUSE_FS
>>>>          If you want to develop a userspace FS, or if you want to use
>>>>          a filesystem based on FUSE, answer Y or M.
>>>>    +config FUSE_READDIR_ORDER
>>>> +    int
>>>> +    range 0 5
>>>> +    default 5
>>>> +    help
>>>> +        readdir performance varies greatly depending on the size of
>>>> the read.
>>>> +        Larger buffers results in larger reads, thus fewer reads and
>>>> higher
>>>> +        performance in return.
>>>> +
>>>> +        You may want to reduce this value on seriously constrained
>>>> memory
>>>> +        systems where 128KiB (assuming 4KiB pages) cache pages is
>>>> not ideal.
>>>> +
>>>> +        This value reprents the order of the number of pages to
>>>> allocate (ie,
>>>> +        the shift value).  A value of 0 is thus 1 page (4KiB) where
>>>> 5 is 32
>>>> +        pages (128KiB).
>>>> +
>>> I like the idea of a larger readdir size, but shouldn't that be a
>>> server/daemon/library decision which size to use, instead of kernel
>>> compile time? So should be part of FUSE_INIT negotiation?
>> Yes sure, but there still needs to be a default.  And one page at a time
>> doesn't cut it.
> With FUSE_INIT userspace would make that decision, based on what kernel
> fuse suggests? process_init_reply() already handles other limits - I
> don't see why readdir max has to be compile time option. Maybe a module
> option to set the limit?
>
> Thanks,
> Bernd

I had similar question / comment. This seems to me to be more 
appropriately handed by the server via FUSE_INIT.

And wouldn't "max" more easily be FUSE_MAX_MAX_PAGES? Is there a reason 
not to allow upwards of 256 pages sized readdir buffer?