linux-kernel - Re: [PATCH 6.10 000/809] 6.10.3-rc3 review

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Message-ID: <bd654d0a-6ded-4ebf-a2ae-d2e1e99adb93@suse.cz>
Date: Tue, 6 Aug 2024 21:40:30 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
 Guenter Roeck <linux@...ck-us.net>
Cc: Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 linux-kernel@...r.kernel.org, Linux-MM <linux-mm@...ck.org>,
 Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 6.10 000/809] 6.10.3-rc3 review

On 8/6/24 21:21, Vlastimil Babka wrote:
> On 8/6/24 20:23, Linus Torvalds wrote:
>> On Tue, 6 Aug 2024 at 11:13, Guenter Roeck <linux@...ck-us.net> wrote:
>>>
>>> On 8/6/24 10:49, Linus Torvalds wrote:
>>> > [ Adding s390 people, this is strange ]
>>>
>>> Did I get lost somewhere ? I am seeing this with parisc (64 bit), not s390.
>> 
>> Duh. Sorry for the noise. I don't know why I thought this was s390.
>> 
>> The parisc __ffs() is also using some grotty inline asm, but I don't
>> see how the compiler could make a mess of it.
> 
> Note the alignment rules only apply to generic kmalloc-* caches, not "named"
> specific caches, such as kmem_cache and kmem_cache_node.

Also to clarify why objsize looks odd in the slabinfo for the kmalloc
caches, e.g. kmalloc-64 has 256 etc. That's also not because of wrong
alignment calculations, but because full slub_debug is enabled for
everything (CONFIG_SLUB_DEBUG_ON=y) so there's lots of metadata, redzones
etc. (it's also why these consistency checks are executed). The column says
<objsize> but it's actually reporting the full s->size, not only the actual
object...

>>                 Linus
>