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/

Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Yu Ma <yu.ma@intel.com>
---
v1 -> v2:
- Update vma_link() to reduce the hold time on file mapping lock as well.
Based on v6.4-rc7, vma_link() is only called by insert_vm_struct ()
and copy_vma(), which are both protected by mmap_lock.
---
 mm/mmap.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index d600404580b2..6f42ca2ab84a 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -444,14 +444,11 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
 	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);
 	}
@@ -2708,12 +2705,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	if (vma_iter_prealloc(&vmi))
 		goto close_and_free_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);
 
-- 
2.39.3

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.

Thanks.

> -----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

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@intel.com/

Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Yu Ma <yu.ma@intel.com>
---
v2 -> v3: Rebase the patch to v6.5-rc1, which includes 1c7873e3364 (mm:
lock newly mapped VMA with corrected ordering), and update commit
message to status on v6.5-rc1
v1 -> v2: Update vma_link() to reduce the hold time on file mapping lock
as well. Based on v6.5-rc1, vma_link() is only called by
insert_vm_struct () and copy_vma(), which are both protected by mmap_lock.
---
---
 mm/mmap.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 3eda23c9ebe7..ce31aec82e82 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -412,14 +412,11 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
 	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 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 
 	/* 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);
 
-- 
2.39.3