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

["Ma, Yu" <yu.ma@intel.com>]

> -----Original Message-----
> From: Andrew Morton <akpm@linux-foundation.org>
> Sent: Wednesday, July 12, 2023 2:28 AM
> To: Ma, Yu <yu.ma@intel.com>
> Cc: Liam.Howlett@Oracle.com; kirill@shutemov.name; Williams, Dan J
> <dan.j.williams@intel.com>; Hansen, Dave <dave.hansen@intel.com>; linux-
> kernel@vger.kernel.org; linux-mm@kvack.org; Zhu, Lipeng
> <lipeng.zhu@intel.com>; Deng, Pan <pan.deng@intel.com>;
> shakeelb@google.com; Li, Tianyou <tianyou.li@intel.com>; Chen, Tim C
> <tim.c.chen@intel.com>; tim.c.chen@linux.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@intel.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.
> 
OK, no problem.


Regards
Yu