linux-kernel - Re: [PATCH v3 0/8] make slab shrink lockless

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

Message-ID: <c949c89a-0b0d-723f-4c60-f6374b1993f3@bytedance.com>
Date:   Tue, 28 Feb 2023 18:11:34 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, tkhai@...ru,
        hannes@...xchg.org, shakeelb@...gle.com, mhocko@...nel.org,
        muchun.song@...ux.dev, david@...hat.com, shy828301@...il.com,
        sultan@...neltoast.com, dave@...olabs.net,
        penguin-kernel@...ove.SAKURA.ne.jp, paulmck@...nel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/8] make slab shrink lockless



On 2023/2/28 03:02, Roman Gushchin wrote:
> On Mon, Feb 27, 2023 at 09:31:51PM +0800, Qi Zheng wrote:
>>
>>
>> On 2023/2/27 03:51, Andrew Morton wrote:
>>> On Sun, 26 Feb 2023 22:46:47 +0800 Qi Zheng <zhengqi.arch@...edance.com> wrote:
>>>
>> Save the above script, then run test and touch commands.
>>
>> Then we can use the following perf command to view hotspots:
>>
>> perf top -U -F 999
>>
>> 1) Before applying this patchset:
>>
>>    32.31%  [kernel]           [k] down_read_trylock
>>    19.40%  [kernel]           [k] pv_native_safe_halt
>>    16.24%  [kernel]           [k] up_read
>>    15.70%  [kernel]           [k] shrink_slab
>>     4.69%  [kernel]           [k] _find_next_bit
>>     2.62%  [kernel]           [k] shrink_node
>>     1.78%  [kernel]           [k] shrink_lruvec
>>     0.76%  [kernel]           [k] do_shrink_slab
>>
>> 2) After applying this patchset:
>>
>>    27.83%  [kernel]           [k] _find_next_bit
>>    16.97%  [kernel]           [k] shrink_slab
>>    15.82%  [kernel]           [k] pv_native_safe_halt
>>     9.58%  [kernel]           [k] shrink_node
>>     8.31%  [kernel]           [k] shrink_lruvec
>>     5.64%  [kernel]           [k] do_shrink_slab
>>     3.88%  [kernel]           [k] mem_cgroup_iter
> 
> Not opposing the intention of the patchset in any way (I actually think
> it's a good idea to make the shrinkers list lockless), but looking at
> both outputs above I think that the main problem is not the contention on
> the semaphore, but the reason of this contention.

Yes, in the above scenario, there is indeed no lock contention problem.

> 
> It seems like often there is a long list of shrinkers which barely
> can reclaim any memory, but we're calling them again and again.
> In order to achieve real wins with real-life workloads, I guess
> it's what we should optimize.
> 
> Thanks!

-- 
Thanks,
Qi