linux-kernel - Re: [PATCH] mm/slub: embed __slab

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <30743bfa-fbbb-c091-3b6e-dc24975fc6c3@suse.cz>
Date:   Fri, 5 Feb 2021 14:03:57 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Abel Wu <abel.w@...oud.com>, Christoph Lameter <cl@...ux.com>
Cc:     Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        hewenliang4@...wei.com, wuyun.wu@...wei.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/slub: embed __slab_alloc to its caller

On 2/3/21 2:41 AM, Abel Wu wrote:
>> On Feb 2, 2021, at 6:11 PM, Christoph Lameter <cl@...ux.com> wrote:
>> 
>> On Tue, 2 Feb 2021, Abel Wu wrote:
>> 
>>> Since slab_alloc_node() is the only caller of __slab_alloc(), embed
>>> __slab_alloc() to its caller to save function call overhead. This
>>> will also expand the caller's code block size a bit, but hackbench
>>> tests on both host and guest didn't show a difference w/ or w/o
>>> this patch.
>> 
>> slab_alloc_node is an always_inline function. It is intentional that only
>> the fast path was inlined and not the slow path.
> 
> Oh I got it. Thanks for your excellent explanation.

BTW, there's a script in the Linux source to nicely see the effect of such changes:

./scripts/bloat-o-meter slub.o.before mm/slub.o
add/remove: 0/1 grow/shrink: 9/0 up/down: 1660/-1130 (530)
Function                                     old     new   delta
__slab_alloc                                 127    1130   +1003
__kmalloc_track_caller                       877     965     +88
__kmalloc                                    878     966     +88
kmem_cache_alloc                             778     862     +84
__kmalloc_node_track_caller                  996    1080     +84
kmem_cache_alloc_node_trace                  813     896     +83
kmem_cache_alloc_node                        800     881     +81
kmem_cache_alloc_trace                       786     862     +76
__kmalloc_node                               998    1071     +73
___slab_alloc                               1130       -   -1130
Total: Before=57782, After=58312, chg +0.92%

And yeah, bloating all the entry points wouldn't be nice.
Thanks,
Vlastimil