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Date: Wed, 1 Jun 2022 17:56:22 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, Dave Chinner <dchinner@...hat.com>,
linux-kernel@...r.kernel.org,
Kent Overstreet <kent.overstreet@...il.com>,
Hillf Danton <hdanton@...a.com>,
Christophe JAILLET <christophe.jaillet@...adoo.fr>,
Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v5 6/6] mm: shrinkers: add scan interface for shrinker
debugfs
On Wed, Jun 01, 2022 at 02:23:51PM -0700, Andrew Morton wrote:
> On Tue, 31 May 2022 20:22:27 -0700 Roman Gushchin <roman.gushchin@...ux.dev> wrote:
>
> > Add a scan interface which allows to trigger scanning of a particular
> > shrinker and specify memcg and numa node. It's useful for testing,
> > debugging and profiling of a specific scan_objects() callback.
> > Unlike alternatives (creating a real memory pressure and dropping
> > caches via /proc/sys/vm/drop_caches) this interface allows to interact
> > with only one shrinker at once. Also, if a shrinker is misreporting
> > the number of objects (as some do), it doesn't affect scanning.
> >
> > ..
> >
> > --- a/mm/shrinker_debug.c
> > +++ b/mm/shrinker_debug.c
> > @@ -99,6 +99,78 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
> > }
> > DEFINE_SHOW_ATTRIBUTE(shrinker_debugfs_count);
> >
> > +static int shrinker_debugfs_scan_open(struct inode *inode, struct file *file)
> > +{
> > + file->private_data = inode->i_private;
> > + return nonseekable_open(inode, file);
> > +}
> > +
> > +static ssize_t shrinker_debugfs_scan_write(struct file *file,
> > + const char __user *buf,
> > + size_t size, loff_t *pos)
> > +{
> > + struct shrinker *shrinker = file->private_data;
> > + unsigned long nr_to_scan = 0, ino;
> > + struct shrink_control sc = {
> > + .gfp_mask = GFP_KERNEL,
> > + };
> > + struct mem_cgroup *memcg = NULL;
> > + int nid;
> > + char kbuf[72];
> > + int read_len = size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1);
>
> size_t or ulong would be more appropriate.
I agree.
>
> > + ssize_t ret;
> > +
> > + if (copy_from_user(kbuf, buf, read_len))
> > + return -EFAULT;
> > + kbuf[read_len] = '\0';
> > +
> > + if (sscanf(kbuf, "%lu %d %lu", &ino, &nid, &nr_to_scan) < 2)
>
> Was it intentional to permit more than three args?
Good catch! No, of course it wasn't intentional.
Below is an updated version of this patch.
Thank you for taking a look!
--
>From b8f0b0fd5bcbc907dfedf2609743713ba8093e31 Mon Sep 17 00:00:00 2001
From: Roman Gushchin <roman.gushchin@...ux.dev>
Date: Fri, 6 May 2022 11:40:36 -0700
Subject: [PATCH v5 6/6] mm: shrinkers: add scan interface for shrinker debugfs
Add a scan interface which allows to trigger scanning of a particular
shrinker and specify memcg and numa node. It's useful for testing,
debugging and profiling of a specific scan_objects() callback.
Unlike alternatives (creating a real memory pressure and dropping
caches via /proc/sys/vm/drop_caches) this interface allows to interact
with only one shrinker at once. Also, if a shrinker is misreporting
the number of objects (as some do), it doesn't affect scanning.
Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
Acked-by: Muchun Song <songmuchun@...edance.com>
---
.../admin-guide/mm/shrinker_debugfs.rst | 39 +++++++++-
mm/shrinker_debug.c | 74 +++++++++++++++++++
2 files changed, 109 insertions(+), 4 deletions(-)
diff --git a/Documentation/admin-guide/mm/shrinker_debugfs.rst b/Documentation/admin-guide/mm/shrinker_debugfs.rst
index 1e0e5bdb8179..3887f0b294fe 100644
--- a/Documentation/admin-guide/mm/shrinker_debugfs.rst
+++ b/Documentation/admin-guide/mm/shrinker_debugfs.rst
@@ -5,14 +5,16 @@ Shrinker Debugfs Interface
==========================
Shrinker debugfs interface provides a visibility into the kernel memory
-shrinkers subsystem and allows to get information about individual shrinkers.
+shrinkers subsystem and allows to get information about individual shrinkers
+and interact with them.
For each shrinker registered in the system a directory in **<debugfs>/shrinker/**
is created. The directory's name is composed from the shrinker's name and an
unique id: e.g. *kfree_rcu-0* or *sb-xfs:vda1-36*.
-Each shrinker directory contains the **count** file, which allows to trigger
-the *count_objects()* callback for each memcg and numa node (if applicable).
+Each shrinker directory contains **count** and **scan** files, which allow to
+trigger *count_objects()* and *scan_objects()* callbacks for each memcg and
+numa node (if applicable).
Usage:
------
@@ -43,7 +45,7 @@ Usage:
$ cd sb-btrfs\:vda2-24/
$ ls
- count
+ count scan
3. *Count objects*
@@ -102,3 +104,32 @@ Usage:
2877 84 0
293 1 0
735 8 0
+
+4. *Scan objects*
+
+ The expected input format::
+
+ <cgroup inode id> <numa id> <number of objects to scan>
+
+ For a non-memcg-aware shrinker or on a system with no memory
+ cgrups **0** should be passed as cgroup id.
+ ::
+
+ $ cd /sys/kernel/debug/shrinker/
+ $ cd sb-btrfs\:vda2-24/
+
+ $ cat count | head -n 5
+ 1 212 0
+ 21 97 0
+ 55 802 5
+ 2367 2 0
+ 225 13 0
+
+ $ echo "55 0 200" > scan
+
+ $ cat count | head -n 5
+ 1 212 0
+ 21 96 0
+ 55 752 5
+ 2367 2 0
+ 225 13 0
diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index 781ecbd3d608..12026472daae 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -99,6 +99,78 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
}
DEFINE_SHOW_ATTRIBUTE(shrinker_debugfs_count);
+static int shrinker_debugfs_scan_open(struct inode *inode, struct file *file)
+{
+ file->private_data = inode->i_private;
+ return nonseekable_open(inode, file);
+}
+
+static ssize_t shrinker_debugfs_scan_write(struct file *file,
+ const char __user *buf,
+ size_t size, loff_t *pos)
+{
+ struct shrinker *shrinker = file->private_data;
+ unsigned long nr_to_scan = 0, ino, read_len;
+ struct shrink_control sc = {
+ .gfp_mask = GFP_KERNEL,
+ };
+ struct mem_cgroup *memcg = NULL;
+ int nid;
+ char kbuf[72];
+ ssize_t ret;
+
+ read_len = size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1);
+ if (copy_from_user(kbuf, buf, read_len))
+ return -EFAULT;
+ kbuf[read_len] = '\0';
+
+ if (sscanf(kbuf, "%lu %d %lu", &ino, &nid, &nr_to_scan) != 2)
+ return -EINVAL;
+
+ if (nid < 0 || nid >= nr_node_ids)
+ return -EINVAL;
+
+ if (nr_to_scan == 0)
+ return size;
+
+ if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
+ memcg = mem_cgroup_get_from_ino(ino);
+ if (!memcg || IS_ERR(memcg))
+ return -ENOENT;
+
+ if (!mem_cgroup_online(memcg)) {
+ mem_cgroup_put(memcg);
+ return -ENOENT;
+ }
+ } else if (ino != 0) {
+ return -EINVAL;
+ }
+
+ ret = down_read_killable(&shrinker_rwsem);
+ if (ret) {
+ mem_cgroup_put(memcg);
+ return ret;
+ }
+
+ sc.nid = nid;
+ sc.memcg = memcg;
+ sc.nr_to_scan = nr_to_scan;
+ sc.nr_scanned = nr_to_scan;
+
+ shrinker->scan_objects(shrinker, &sc);
+
+ up_read(&shrinker_rwsem);
+ mem_cgroup_put(memcg);
+
+ return size;
+}
+
+static const struct file_operations shrinker_debugfs_scan_fops = {
+ .owner = THIS_MODULE,
+ .open = shrinker_debugfs_scan_open,
+ .write = shrinker_debugfs_scan_write,
+};
+
int shrinker_debugfs_add(struct shrinker *shrinker)
{
struct dentry *entry;
@@ -128,6 +200,8 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
debugfs_create_file("count", 0220, entry, shrinker,
&shrinker_debugfs_count_fops);
+ debugfs_create_file("scan", 0440, entry, shrinker,
+ &shrinker_debugfs_scan_fops);
return 0;
}
--
2.35.3
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