linux-kernel - Re: [PATCH] mm: slub: do not warn when allocating slab obj extensions fails

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Message-ID: <da5a2a97-060d-441d-b66d-9a0dd6bb7a7a@gmail.com>
Date: Wed, 21 May 2025 17:21:28 +0100
From: Usama Arif <usamaarif642@...il.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, hannes@...xchg.org,
 shakeel.butt@...ux.dev, vlad.wing@...il.com, linux-mm@...ck.org,
 kent.overstreet@...ux.dev, cl@...two.org, rientjes@...gle.com,
 vbabka@...e.cz, roman.gushchin@...ux.dev, harry.yoo@...cle.com,
 linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH] mm: slub: do not warn when allocating slab obj extensions
 fails



On 21/05/2025 17:02, Suren Baghdasaryan wrote:
> On Wed, May 21, 2025 at 7:25 AM Usama Arif <usamaarif642@...il.com> wrote:
>>
>> In memory bound systems, a large number of warnings for failing this
>> allocation repeatedly may mask any real issues in the system
>> during memory pressure being reported in dmesg. Failing this
>> allocation is not indicative of a bug, so remove the warning.
>>
>> Signed-off-by: Usama Arif <usamaarif642@...il.com>
>> Reported-by: Vlad Poenaru <vlad.wing@...il.com>
>> Closes: https://lore.kernel.org/all/17fab2d6-5a74-4573-bcc3-b75951508f0a@gmail.com/
>> ---
>> v1 -> v2:
>> - remove the warning completely. We will have a way in the
>>   future to indicate that the mem alloc profile is inaccurate.
>> ---
>>  mm/slub.c | 4 +---
>>  1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index dc9e729e1d26..06ab9a558b73 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -2102,9 +2102,7 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
>>
>>         slab = virt_to_slab(p);
>>         if (!slab_obj_exts(slab) &&
>> -           WARN(alloc_slab_obj_exts(slab, s, flags, false),
>> -                "%s, %s: Failed to create slab extension vector!\n",
>> -                __func__, s->name))
>> +           alloc_slab_obj_exts(slab, s, flags, false))
> 
> I thought we agreed to having pr_warn_once() here. Did I miss something?
> 

I had [1] yesterday but I saw Johannes's mail [2] in and Harry mentioned in [3] that
failing to allocate the extension vector can happen during normal operations. So I
thought maybe there are more votes for removing it.

I am ok with either pr_warn_once or removing it completely.

I guess the question is, is it considered OK to fail here?

[1] https://lore.kernel.org/all/64b19c8f-e02e-490b-b987-9a996f36be21@gmail.com/
[2] https://lore.kernel.org/all/20250520171814.GC773385@cmpxchg.org/
[3] https://lore.kernel.org/all/20250520171814.GC773385@cmpxchg.org/