Re: [PATCH 2/3] fs: fsnotify: account fsnotify metadata to kmemcg

From: Shakeel Butt
Date: Tue Jun 19 2018 - 10:15:42 EST

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On Tue, Jun 19, 2018 at 12:20 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> On Tue, Jun 19, 2018 at 8:13 AM, Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
> > A lot of memory can be consumed by the events generated for the huge or
> > unlimited queues if there is either no or slow listener. This can cause
> > system level memory pressure or OOMs. So, it's better to account the
> > fsnotify kmem caches to the memcg of the listener.
> >
> > There are seven fsnotify kmem caches and among them allocations from
> > dnotify_struct_cache, dnotify_mark_cache, fanotify_mark_cache and
> > inotify_inode_mark_cachep happens in the context of syscall from the
> > listener. So, SLAB_ACCOUNT is enough for these caches.
> >
> > The objects from fsnotify_mark_connector_cachep are not accounted as they
> > are small compared to the notification mark or events and it is unclear
> > whom to account connector to since it is shared by all events attached to
> > the inode.
> >
> > The allocations from the event caches happen in the context of the event
> > producer. For such caches we will need to remote charge the allocations
> > to the listener's memcg. Thus we save the memcg reference in the
> > fsnotify_group structure of the listener.
> >
> > This patch has also moved the members of fsnotify_group to keep the size
> > same, at least for 64 bit build, even with additional member by filling
> > the holes.
> >
> > Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> > Acked-by: Jan Kara <jack@xxxxxxx>
> > Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> > Cc: Amir Goldstein <amir73il@xxxxxxxxx>
> > Cc: Christoph Lameter <cl@xxxxxxxxx>
> > Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> > Cc: David Rientjes <rientjes@xxxxxxxxxx>
> > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > Cc: Greg Thelen <gthelen@xxxxxxxxxx>
> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> > Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
> > Cc: Mel Gorman <mgorman@xxxxxxx>
> > Cc: Vlastimil Babka <vbabka@xxxxxxx>
> > Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > ---
> > Changelog since v5:
> > - None
> >
> > Changelog since v4:
> > - Fixed the build for CONFIG_MEMCG=n
> >
> > Changelog since v3:
> > - Rebased over Jan's patches.
> > - Some cleanup based on Amir's comments.
> >
> > Changelog since v2:
> > - None
> >
> > Changelog since v1:
> > - no more charging fsnotify_mark_connector objects
> > - Fixed the build for SLOB
> >
> > fs/notify/dnotify/dnotify.c | 5 +++--
> > fs/notify/fanotify/fanotify.c | 6 ++++--
> > fs/notify/fanotify/fanotify_user.c | 5 ++++-
> > fs/notify/group.c | 6 ++++++
> > fs/notify/inotify/inotify_fsnotify.c | 2 +-
> > fs/notify/inotify/inotify_user.c | 5 ++++-
> > include/linux/fsnotify_backend.h | 12 ++++++++----
> > include/linux/memcontrol.h | 7 +++++++
> > mm/memcontrol.c | 15 +++++++++++++--
> > 9 files changed, 50 insertions(+), 13 deletions(-)
> >
> > diff --git a/fs/notify/dnotify/dnotify.c b/fs/notify/dnotify/dnotify.c
> > index e2bea2ac5dfb..a6365e6bc047 100644
> > --- a/fs/notify/dnotify/dnotify.c
> > +++ b/fs/notify/dnotify/dnotify.c
> > @@ -384,8 +384,9 @@ int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
> >
> > static int __init dnotify_init(void)
> > {
> > - dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC);
> > - dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC);
> > + dnotify_struct_cache = KMEM_CACHE(dnotify_struct,
> > + SLAB_PANIC|SLAB_ACCOUNT);
> > + dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC|SLAB_ACCOUNT);
> >
> > dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
> > if (IS_ERR(dnotify_group))
> > diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> > index f90842efea13..c8d6e37a4855 100644
> > --- a/fs/notify/fanotify/fanotify.c
> > +++ b/fs/notify/fanotify/fanotify.c
> > @@ -154,14 +154,16 @@ struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
> > if (fanotify_is_perm_event(mask)) {
> > struct fanotify_perm_event_info *pevent;
> >
> > - pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
> > + pevent = kmem_cache_alloc_memcg(fanotify_perm_event_cachep, gfp,
> > + group->memcg);
> > if (!pevent)
> > return NULL;
> > event = &pevent->fae;
> > pevent->response = 0;
> > goto init;
> > }
> > - event = kmem_cache_alloc(fanotify_event_cachep, gfp);
> > + event = kmem_cache_alloc_memcg(fanotify_event_cachep, gfp,
> > + group->memcg);
> > if (!event)
> > return NULL;
> > init: __maybe_unused
> > diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> > index ec4d8c59d0e3..0cf45041dc32 100644
> > --- a/fs/notify/fanotify/fanotify_user.c
> > +++ b/fs/notify/fanotify/fanotify_user.c
> > @@ -16,6 +16,7 @@
> > #include <linux/uaccess.h>
> > #include <linux/compat.h>
> > #include <linux/sched/signal.h>
> > +#include <linux/memcontrol.h>
> >
> > #include <asm/ioctls.h>
> >
> > @@ -756,6 +757,7 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
> >
> > group->fanotify_data.user = user;
> > atomic_inc(&user->fanotify_listeners);
> > + group->memcg = get_mem_cgroup_from_mm(current->mm);
> >
>
> It seem to me that you should export a wrapper to modules with
> the mem_cgroup_ prefix and not sure that need to pass current->mm
> to this wrapper.
>

Thanks, I will test with fsnotify as module.

> > oevent = fanotify_alloc_event(group, NULL, FS_Q_OVERFLOW, NULL);
> > if (unlikely(!oevent)) {
> > @@ -957,7 +959,8 @@ COMPAT_SYSCALL_DEFINE6(fanotify_mark,
> > */
> > static int __init fanotify_user_setup(void)
> > {
> > - fanotify_mark_cache = KMEM_CACHE(fsnotify_mark, SLAB_PANIC);
> > + fanotify_mark_cache = KMEM_CACHE(fsnotify_mark,
> > + SLAB_PANIC|SLAB_ACCOUNT);
> > fanotify_event_cachep = KMEM_CACHE(fanotify_event_info, SLAB_PANIC);
> > if (IS_ENABLED(CONFIG_FANOTIFY_ACCESS_PERMISSIONS)) {
> > fanotify_perm_event_cachep =
> > diff --git a/fs/notify/group.c b/fs/notify/group.c
> > index aa5468f23e45..300fc0f62115 100644
> > --- a/fs/notify/group.c
> > +++ b/fs/notify/group.c
> > @@ -22,6 +22,7 @@
> > #include <linux/srcu.h>
> > #include <linux/rculist.h>
> > #include <linux/wait.h>
> > +#include <linux/memcontrol.h>
> >
> > #include <linux/fsnotify_backend.h>
> > #include "fsnotify.h"
> > @@ -36,6 +37,11 @@ static void fsnotify_final_destroy_group(struct fsnotify_group *group)
> > if (group->ops->free_group_priv)
> > group->ops->free_group_priv(group);
> >
> > +#ifdef CONFIG_MEMCG
> > + if (group->memcg)
> > + css_put(&group->memcg->css);
> > +#endif
> > +
>
> This looks very much like an internal implementation detail that has no
> business in an external module. I see evidence that you have used
> mem_cgroup_put() in the patch at some point and I agree that you
> need to export a pair of matching helpers to external modules.
>

Do not worry. Andrew will change this to mem_cgroup_put(). Basically
mem_cgroup_put() was defined by still-in-review patch series by Roman.
There were build failure reports where someone was taking this series
either without Roman's series or applying series out of order.

thanks,
Shakeel

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