linux-kernel - Re: [PATCH] mm/smaps_rollup: return empty file for kthreads instead of ESRCH

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Message-Id: <1649949601.z8rr7ed5qb.none@localhost>
Date:   Thu, 14 Apr 2022 11:24:35 -0400
From:   "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Colascione <dancol@...gle.com>,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm/smaps_rollup: return empty file for kthreads instead
 of ESRCH

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 regression.

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

Cheers,
Alex.