linux-kernel - Re: EMFILE/ENFILE mitigation needed in erofs?

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Message-ID: <YmGfhFQshWOkAqNG@B-P7TQMD6M-0146.local>
Date:   Fri, 22 Apr 2022 02:16:36 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     David Howells <dhowells@...hat.com>
Cc:     JeffleXu <jefflexu@...ux.alibaba.com>, linux-cachefs@...hat.com,
        xiang@...nel.org, chao@...nel.org, linux-erofs@...ts.ozlabs.org,
        torvalds@...ux-foundation.org, gregkh@...uxfoundation.org,
        willy@...radead.org, linux-fsdevel@...r.kernel.org,
        joseph.qi@...ux.alibaba.com, bo.liu@...ux.alibaba.com,
        tao.peng@...ux.alibaba.com, gerry@...ux.alibaba.com,
        eguan@...ux.alibaba.com, linux-kernel@...r.kernel.org,
        luodaowen.backend@...edance.com, tianzichen@...ishou.com,
        fannaihao@...du.com, zhangjiachen.jaycee@...edance.com
Subject: Re: EMFILE/ENFILE mitigation needed in erofs?

Hi David,

On Thu, Apr 21, 2022 at 06:57:40PM +0100, David Howells wrote:
> JeffleXu <jefflexu@...ux.alibaba.com> wrote:
> 
> > 2. Our user daemon will configure rlimit-nofile to a reasonably large
> > (e.g. 1 million) value, so that it won't fail when trying to allocate fds.
> 
> There's a system-wide limit also; simply increasing the rlimit won't override
> that.

Yes, I suggest that we should add some words to document this
to system administrators to take care of `/proc/sys/fs/file-max',
but I think it's typically not a problem about our on-demand cases.

Since each cookie equals to an erofs device, so not too many erofs
devices (much like docker layers) for one erofs images and they
are all handled when mounting (which needs privilege permissions.)

And due to this, fscache dir can be easily backed up, restored, and
transfered since they are really golden erofs image files.

Thanks,
Gao Xiang

> 
> David