linux-kernel - Re: [RFC 02/26] mm, slub: allocate private object map for validate_slab

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Date:   Tue, 8 Jun 2021 12:37:30 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [RFC 02/26] mm, slub: allocate private object map for
 validate_slab_cache()

On 5/25/21 1:33 PM, Mel Gorman wrote:
> On Tue, May 25, 2021 at 12:36:52PM +0200, Vlastimil Babka wrote:
>> > Most callers of validate_slab_cache don't care about the return value
>> > except when the validate sysfs file is written. Should a simply
>> > informational message be displayed for -ENOMEM in case a writer to
>> > validate fails and it's not obvious it was because of an allocation
>> > failure?
>> 
>> he other callers are all in the effectively dead resiliency_test() code, which
>> has meanwhile been replaced in mmotm by kunit tests meanwhile. But it's true
>> those don't check the results either for now.
>> 
> 
> Ok.
> 
>> > It's a fairly minor concern so whether you add a message or not
>> 
>> I think I'll rather fix up the tests. Or do you mean that -ENOMEM for a sysfs
>> write is also not enough and there should be a dmesg explanation for that case?
>> 
> 
> I mean the -ENOMEM for a sysfs write. While it's very unlikely, it might
> would explain an unexpected write failure.

On second thought, a failed GFP_KERNEL allocation will already generate a
prominent warning, so an extra message looks arbitrary.