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

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Message-ID: <3d0a1483-3491-4c10-b19b-42bf0dace79e@gmail.com>
Date: Wed, 21 May 2025 17:39:19 +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 17:29, Suren Baghdasaryan wrote:
> On Wed, May 21, 2025 at 9:21 AM Usama Arif <usamaarif642@...il.com> wrote:
>>
>>
>>
>> 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 feel like we should have at least some indication that something
> went wrong here.
> 
>>
>> I guess the question is, is it considered OK to fail here?
> 
> Well, it's not ok but not catastrophic either, so warning seems
> appropriate to me.
> 
Ok, I will wait a couple of days incase someone has any objections and send
https://lore.kernel.org/all/64b19c8f-e02e-490b-b987-9a996f36be21@gmail.com/
as v3.

Thanks!

>>
>> [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/