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UPSTREAM: mm: add anonymous vma name refcounting

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While forking a process with high number (64K) of named anonymous vmas
the overhead caused by strdup() is noticeable.  Experiments with ARM64
Android device show up to 40% performance regression when forking a
process with 64k unpopulated anonymous vmas using the max name lengths
vs the same process with the same number of anonymous vmas having no
name.

Introduce anon_vma_name refcounted structure to avoid the overhead of
copying vma names during fork() and when splitting named anonymous vmas.

When a vma is duplicated, instead of copying the name we increment the
refcount of this structure.  Multiple vmas can point to the same
anon_vma_name as long as they increment the refcount.  The name member
of anon_vma_name structure is assigned at structure allocation time and
is never changed.  If vma name changes then the refcount of the original
structure is dropped, a new anon_vma_name structure is allocated to hold
the new name and the vma pointer is updated to point to the new
structure.

With this approach the fork() performance regressions is reduced 3-4x
times and with usecases using more reasonable number of VMAs (a few
thousand) the regressions is not measurable.

Link: https://lkml.kernel.org/r/20211019215511.3771969-3-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Colin Cross <ccross@google.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jan Glauber <jan.glauber@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rob Landley <rob@landley.net>
Cc: "Serge E. Hallyn" <serge.hallyn@ubuntu.com>
Cc: Shaohua Li <shli@fusionio.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

(cherry picked from commit 78db341283)

Bug: 120441514
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: I4b6d63b1aced3813ebb91479f4bcfd0d89e8fa29
This commit is contained in:
Suren Baghdasaryan
2022-01-14 14:06:03 -08:00
parent 301c56064d
commit 3f4e41d409
2 changed files with 44 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
include/linux/mm_types.h
View File

@@ -5,6 +5,7 @@
#include <linux/mm_types_task.h>
#include <linux/auxvec.h>
#include <linux/kref.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/rbtree.h>
@@ -310,6 +311,12 @@ struct vm_userfaultfd_ctx {
struct vm_userfaultfd_ctx {};
#endif /* CONFIG_USERFAULTFD */
struct anon_vma_name {
struct kref kref;
/* The name needs to be at the end because it is dynamically sized. */
char name[];
};
/*
* This struct describes a virtual memory area. There is one of these
* per VM-area/task. A VM area is any part of the process virtual memory
@@ -361,7 +368,7 @@ struct vm_area_struct {
unsigned long rb_subtree_last;
} shared;
/* Serialized by mmap_sem. */
char *anon_name;
struct anon_vma_name *anon_name;
};
/*

42
mm/madvise.c
View File

@@ -64,6 +64,29 @@ static int madvise_need_mmap_write(int behavior)
}
#ifdef CONFIG_ANON_VMA_NAME
static struct anon_vma_name *anon_vma_name_alloc(const char *name)
{
struct anon_vma_name *anon_name;
size_t count;
/* Add 1 for NUL terminator at the end of the anon_name->name */
count = strlen(name) + 1;
anon_name = kmalloc(struct_size(anon_name, name, count), GFP_KERNEL);
if (anon_name) {
kref_init(&anon_name->kref);
memcpy(anon_name->name, name, count);
}
return anon_name;
}
static void vma_anon_name_free(struct kref *kref)
{
struct anon_vma_name *anon_name =
container_of(kref, struct anon_vma_name, kref);
kfree(anon_name);
}
static inline bool has_vma_anon_name(struct vm_area_struct *vma)
{
return !vma->vm_file && vma->anon_name;
@@ -76,7 +99,7 @@ const char *vma_anon_name(struct vm_area_struct *vma)
mmap_assert_locked(vma->vm_mm);
return vma->anon_name;
return vma->anon_name->name;
}
void dup_vma_anon_name(struct vm_area_struct *orig_vma,
@@ -85,34 +108,41 @@ void dup_vma_anon_name(struct vm_area_struct *orig_vma,
if (!has_vma_anon_name(orig_vma))
return;
new_vma->anon_name = kstrdup(orig_vma->anon_name, GFP_KERNEL);
kref_get(&orig_vma->anon_name->kref);
new_vma->anon_name = orig_vma->anon_name;
}
void free_vma_anon_name(struct vm_area_struct *vma)
{
struct anon_vma_name *anon_name;
if (!has_vma_anon_name(vma))
return;
kfree(vma->anon_name);
anon_name = vma->anon_name;
vma->anon_name = NULL;
kref_put(&anon_name->kref, vma_anon_name_free);
}
/* mmap_lock should be write-locked */
static int replace_vma_anon_name(struct vm_area_struct *vma, const char *name)
{
const char *anon_name;
if (!name) {
free_vma_anon_name(vma);
return 0;
}
if (vma->anon_name) {
anon_name = vma_anon_name(vma);
if (anon_name) {
/* Same name, nothing to do here */
if (!strcmp(name, vma->anon_name))
if (!strcmp(name, anon_name))
return 0;
free_vma_anon_name(vma);
}
vma->anon_name = kstrdup(name, GFP_KERNEL);
vma->anon_name = anon_vma_name_alloc(name);
if (!vma->anon_name)
return -ENOMEM;