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Date:   Thu, 14 Apr 2022 11:24:35 -0400
From:   "Alex Xu (Hello71)" <alex_y_xu@yahoo.ca>
Subject: Re: [PATCH] mm/smaps_rollup: return empty file for kthreads instead
 of ESRCH
To:     Alexey Dobriyan <adobriyan@gmail.com>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Daniel Colascione <dancol@google.com>,
        linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Vlastimil Babka <vbabka@suse.cz>
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Excerpts from Alexey Dobriyan's message of April 14, 2022 2:55 am:
> Returning ESRCH is better so that programs don't waste time reading and
> closing empty files and instantiating useless inodes.

Yes, except ESRCH is not returned for open, it is returned for read.

> Of course it is different if this patch was sent as response to a regress=
ion.

I'm not sure I would classify it as a regression; I don't have an=20
existing program which broke, it is a new program which happens to use=20
some functionality which worked with a previous kernel. It is=20
theoretically possible that some program exists that currently uses=20
4.14, and will break if upgraded to 4.19+, but it is also possible that=20
some program exists that currently uses 4.19+ and will break if this=20
patch is applied.

Cheers,
Alex.