linux-kernel - Re: [PATCH] fuse: increase FUSE_MAX_MAX

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Date: Wed, 24 Jan 2024 13:23:26 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: Jingbo Xu <jefflexu@...ux.alibaba.com>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	zhangjiachen.jaycee@...edance.com
Subject: Re: [PATCH] fuse: increase FUSE_MAX_MAX_PAGES limit

On Wed, 24 Jan 2024 at 08:05, Jingbo Xu <jefflexu@...ux.alibaba.com> wrote:
>
> From: Xu Ji <laoji.jx@...baba-inc.com>
>
> Increase FUSE_MAX_MAX_PAGES limit, so that the maximum data size of a
> single request is increased.

The only worry is about where this memory is getting accounted to.
This needs to be thought through, since the we are increasing the
possible memory that an unprivileged user is allowed to pin.



>
> This optimizes the write performance especially when the optimal IO size
> of the backend store at the fuse daemon side is greater than the original
> maximum request size (i.e. 1MB with 256 FUSE_MAX_MAX_PAGES and
> 4096 PAGE_SIZE).
>
> Be noted that this only increases the upper limit of the maximum request
> size, while the real maximum request size relies on the FUSE_INIT
> negotiation with the fuse daemon.
>
> Signed-off-by: Xu Ji <laoji.jx@...baba-inc.com>
> Signed-off-by: Jingbo Xu <jefflexu@...ux.alibaba.com>
> ---
> I'm not sure if 1024 is adequate for FUSE_MAX_MAX_PAGES, as the
> Bytedance floks seems to had increased the maximum request size to 8M
> and saw a ~20% performance boost.

The 20% is against the 256 pages, I guess.  It would be interesting to
see the how the number of pages per request affects performance and
why.

Thanks,
Miklos