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Message-ID: <YmNWfgh5/WEwUkFi@carbon>
Date: Fri, 22 Apr 2022 18:29:34 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Hillf Danton <hdanton@...a.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
Dave Chinner <dchinner@...hat.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/7] mm: introduce memcg interfaces for shrinker
debugfs
On Sat, Apr 23, 2022 at 08:35:52AM +0800, Hillf Danton wrote:
> On Fri, 22 Apr 2022 13:26:40 -0700 Roman Gushchin wrote:
> > This commit introduces "count_memcg" and "scan_memcg" interfaces
> > for memcg-aware shrinkers.
> >
> > Count_memcg using the following format:
> > <cgroup inode number1> <count2>
> > <cgroup inode number2> <count2>
> > ...
> >
> > Memory cgroups with 0 associated objects are skipped.
> >
> > Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
> > ---
> > mm/shrinker_debug.c | 186 +++++++++++++++++++++++++++++++++-----------
> > 1 file changed, 139 insertions(+), 47 deletions(-)
> >
> > diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
> > index 4df7382a0737..002d44d6ad56 100644
> > --- a/mm/shrinker_debug.c
> > +++ b/mm/shrinker_debug.c
> > @@ -1,8 +1,10 @@
> > // SPDX-License-Identifier: GPL-2.0
> > #include <linux/idr.h>
> > +#include <linux/slab.h>
> > #include <linux/debugfs.h>
> > #include <linux/seq_file.h>
> > #include <linux/shrinker.h>
> > +#include <linux/memcontrol.h>
> >
> > /* defined in vmscan.c */
> > extern struct rw_semaphore shrinker_rwsem;
> > @@ -11,25 +13,25 @@ extern struct list_head shrinker_list;
> > static DEFINE_IDA(shrinker_debugfs_ida);
> > static struct dentry *shrinker_debugfs_root;
> >
> > -static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
> > +static unsigned long shrinker_count_objects(struct shrinker *shrinker,
> > + struct mem_cgroup *memcg,
> > + unsigned long *count_per_node)
> > {
> > - struct shrinker *shrinker = (struct shrinker *)m->private;
> > unsigned long nr, total = 0;
> > - int ret, nid;
> > -
> > - ret = down_read_killable(&shrinker_rwsem);
> > - if (ret)
> > - return ret;
> > + int nid;
> >
> > for_each_node(nid) {
> > struct shrink_control sc = {
> > .gfp_mask = GFP_KERNEL,
> > .nid = nid,
> > + .memcg = memcg,
> > };
> >
> > nr = shrinker->count_objects(shrinker, &sc);
> > if (nr == SHRINK_EMPTY)
> > nr = 0;
> > + if (count_per_node)
> > + count_per_node[nid] = nr;
> > total += nr;
> >
> > if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
> > @@ -37,32 +39,17 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
> >
> > cond_resched();
>
> Nit, add a line in response to signal before schedule, given the
> killable above.
Good point, thanks!
>
> > }
> > - up_read(&shrinker_rwsem);
> > -
> > - seq_printf(m, "%lu\n", total);
> >
> > - return ret;
> > + return total;
> > }
> > -DEFINE_SHOW_ATTRIBUTE(shrinker_debugfs_count);
> >
> > -static ssize_t shrinker_debugfs_scan_write(struct file *file,
> > - const char __user *buf,
> > - size_t size, loff_t *pos)
> > +static int shrinker_scan_objects(struct shrinker *shrinker,
> > + struct mem_cgroup *memcg,
> > + unsigned long nr_to_scan)
> > {
> > - struct shrinker *shrinker = (struct shrinker *)file->private_data;
> > - unsigned long nr, total = 0, nr_to_scan;
> > - unsigned long *count_per_node = NULL;
> > - int nid;
> > - char kbuf[24];
> > - int read_len = size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1);
> > - ssize_t ret;
> > -
> > - if (copy_from_user(kbuf, buf, read_len))
> > - return -EFAULT;
> > - kbuf[read_len] = '\0';
> > -
> > - if (kstrtoul(kbuf, 10, &nr_to_scan))
> > - return -EINVAL;
> > + unsigned long *count_per_node;
> > + unsigned long total, nr;
> > + int ret, nid;
> >
> > ret = down_read_killable(&shrinker_rwsem);
> > if (ret)
> > @@ -80,20 +67,7 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
> > goto out;
> > }
> >
> > - for_each_node(nid) {
> > - struct shrink_control sc = {
> > - .gfp_mask = GFP_KERNEL,
> > - .nid = nid,
> > - };
> > -
> > - nr = shrinker->count_objects(shrinker, &sc);
> > - if (nr == SHRINK_EMPTY)
> > - nr = 0;
> > - count_per_node[nid] = nr;
> > - total += nr;
> > -
> > - cond_resched();
> > - }
> > + total = shrinker_count_objects(shrinker, memcg, count_per_node);
> > }
> >
> > for_each_node(nid) {
> > @@ -102,13 +76,13 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
> > .nid = nid,
> > };
> >
> > - if (shrinker->flags & SHRINKER_NUMA_AWARE) {
> > + if (count_per_node) {
> > sc.nr_to_scan = nr_to_scan * count_per_node[nid] /
> > (total ? total : 1);
> > sc.nr_scanned = sc.nr_to_scan;
> > } else {
> > sc.nr_to_scan = nr_to_scan;
> > - sc.nr_scanned = sc.nr_to_scan;
> > + sc.nr_scanned = nr_to_scan;
> > }
> >
> > nr = shrinker->scan_objects(shrinker, &sc);
> > @@ -119,15 +93,51 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
> > break;
> >
> > cond_resched();
> > -
> > }
> > - ret = size;
> > out:
> > up_read(&shrinker_rwsem);
> > kfree(count_per_node);
> > return ret;
> > }
> >
> > +static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
> > +{
> > + struct shrinker *shrinker = (struct shrinker *)m->private;
> > + int ret;
> > +
> > + ret = down_read_killable(&shrinker_rwsem);
> > + if (!ret) {
> > + unsigned long total = shrinker_count_objects(shrinker, NULL, NULL);
> > +
> > + up_read(&shrinker_rwsem);
> > + seq_printf(m, "%lu\n", total);
> > + }
> > + return ret;
> > +}
> > +DEFINE_SHOW_ATTRIBUTE(shrinker_debugfs_count);
> > +
> > +static ssize_t shrinker_debugfs_scan_write(struct file *file,
> > + const char __user *buf,
> > + size_t size, loff_t *pos)
> > +{
> > + struct shrinker *shrinker = (struct shrinker *)file->private_data;
> > + unsigned long nr_to_scan;
> > + char kbuf[24];
> > + int read_len = size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1);
> > + ssize_t ret;
> > +
> > + if (copy_from_user(kbuf, buf, read_len))
> > + return -EFAULT;
> > + kbuf[read_len] = '\0';
> > +
> > + if (kstrtoul(kbuf, 10, &nr_to_scan))
> > + return -EINVAL;
> > +
> > + ret = shrinker_scan_objects(shrinker, NULL, nr_to_scan);
> > +
> > + return ret ? ret : size;
> > +}
> > +
> > static int shrinker_debugfs_scan_open(struct inode *inode, struct file *file)
> > {
> > file->private_data = inode->i_private;
> > @@ -140,6 +150,78 @@ static const struct file_operations shrinker_debugfs_scan_fops = {
> > .write = shrinker_debugfs_scan_write,
> > };
> >
> > +#ifdef CONFIG_MEMCG
> > +static int shrinker_debugfs_count_memcg_show(struct seq_file *m, void *v)
> > +{
> > + struct shrinker *shrinker = (struct shrinker *)m->private;
> > + struct mem_cgroup *memcg;
> > + unsigned long total;
> > + int ret;
> > +
> > + ret = down_read_killable(&shrinker_rwsem);
> > + if (ret)
> > + return ret;
> > + rcu_read_lock();
>
> A minute ... things like cond_resched() or mutex in individual shrinker
> implementation can ruin your nice work within two seconds. The bigger
> pain is can we rule them out from coming shrinkers?
Hm, why? Isn't it the same path as in reclaim? Can you, please, elaborate?
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