linux-kernel - Re: [PATCH v2] mm/mmap: move vma operations to mm_struct out of the critical section of file mapping lock

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Date:   Tue, 11 Jul 2023 11:28:24 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Yu Ma <yu.ma@...el.com>
Cc:     Liam.Howlett@...cle.com, kirill@...temov.name,
        dan.j.williams@...el.com, dave.hansen@...el.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        lipeng.zhu@...el.com, pan.deng@...el.com, shakeelb@...gle.com,
        tianyou.li@...el.com, tim.c.chen@...el.com,
        tim.c.chen@...ux.intel.com
Subject: Re: [PATCH v2] mm/mmap: move vma operations to mm_struct out of the
 critical section of file mapping lock

On Tue, 11 Jul 2023 13:20:20 -0400 Yu Ma <yu.ma@...el.com> wrote:

> UnixBench/Execl represents a class of workload where bash scripts are
> spawned frequently to do some short jobs. When running multiple parallel
> tasks, hot osq_lock is observed from do_mmap and exit_mmap. Both of them
> come from load_elf_binary through the call chain
> "execl->do_execveat_common->bprm_execve->load_elf_binary". In do_mmap,it will
> call mmap_region to create vma node, initialize it and insert it to vma
> maintain structure in mm_struct and i_mmap tree of the mapping file, then
> increase map_count to record the number of vma nodes used. The hot osq_lock
> is to protect operations on file’s i_mmap tree. For the mm_struct member
> change like vma insertion and map_count update, they do not affect i_mmap
> tree. Move those operations out of the lock's critical section, to reduce
> hold time on the lock.
> 
> With this change, on Intel Sapphire Rapids 112C/224T platform, based on
> v6.0-rc6, the 160 parallel score improves by 12%. The patch has no
> obvious performance gain on v6.4-rc4 due to regression of this benchmark
> from this commit f1a7941243c102a44e8847e3b94ff4ff3ec56f25 (mm: convert
> mm's rss stats into percpu_counter). Related discussion and conclusion
> can be referred at the mail thread initiated by 0day as below:
> Link: https://lore.kernel.org/linux-mm/a4aa2e13-7187-600b-c628-7e8fb108def0@intel.com/

Could you please redo/retest this against a kernel which has
1c7873e3364 ("mm: lock newly mapped VMA with corrected ordering")? 
mainline, mm-unstable or linux-next.

Thanks.