The patch titled
Subject: mm/mmap: move vma operations to mm_struct out of the critical section of file mapping lock
has been added to the -mm mm-unstable branch. Its filename is
mm-mmap-move-vma-operations-to-mm_struct-out-of-the-critical-section-of-file-mapping-lock.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mmap-move-vma-operations-to-mm_struct-out-of-the-critical-section-of-file-mapping-lock.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Yu Ma <yu.ma@xxxxxxxxx>
Subject: mm/mmap: move vma operations to mm_struct out of the critical section of file mapping lock
Date: Wed, 12 Jul 2023 10:57:39 -0400
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 v6.5-rc1 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@xxxxxxxxx/
Link: https://lkml.kernel.org/r/20230712145739.604215-1-yu.ma@xxxxxxxxx
Signed-off-by: Yu Ma <yu.ma@xxxxxxxxx>
Reviewed-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Kirill A . Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Zhu, Lipeng <lipeng.zhu@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mmap.c | 11 +++--------
1 file changed, 3 insertions(+), 8 deletions(-)
--- a/mm/mmap.c~mm-mmap-move-vma-operations-to-mm_struct-out-of-the-critical-section-of-file-mapping-lock
+++ a/mm/mmap.c
@@ -412,14 +412,11 @@ static int vma_link(struct mm_struct *mm
if (vma_iter_prealloc(&vmi))
return -ENOMEM;
+ vma_iter_store(&vmi, vma);
+
if (vma->vm_file) {
mapping = vma->vm_file->f_mapping;
i_mmap_lock_write(mapping);
- }
-
- vma_iter_store(&vmi, vma);
-
- if (mapping) {
__vma_link_file(vma, mapping);
i_mmap_unlock_write(mapping);
}
@@ -2811,12 +2808,10 @@ cannot_expand:
/* Lock the VMA since it is modified after insertion into VMA tree */
vma_start_write(vma);
- if (vma->vm_file)
- i_mmap_lock_write(vma->vm_file->f_mapping);
-
vma_iter_store(&vmi, vma);
mm->map_count++;
if (vma->vm_file) {
+ i_mmap_lock_write(vma->vm_file->f_mapping);
if (vma->vm_flags & VM_SHARED)
mapping_allow_writable(vma->vm_file->f_mapping);
_
Patches currently in -mm which might be from yu.ma@xxxxxxxxx are
mm-mmap-move-vma-operations-to-mm_struct-out-of-the-critical-section-of-file-mapping-lock.patch
