The patch titled
Subject: memcg: add comments clarifying aspects of cache attribute propagation
has been added to the -mm tree. Its filename is
memcg-add-comments-clarifying-aspects-of-cache-attribute-propagation.patch
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From: Glauber Costa <glommer@xxxxxxxxxxxxx>
Subject: memcg: add comments clarifying aspects of cache attribute propagation
This patch clarifies two aspects of cache attribute propagation.
First, the expected context for the for_each_memcg_cache macro in
memcontrol.h. The usages already in the codebase are safe. In mm/slub.c,
it is trivially safe because the lock is acquired right before the loop.
In mm/slab.c, it is less so: the lock is acquired by an outer function a
few steps back in the stack, so a VM_BUG_ON() is added to make sure it is
indeed safe.
A comment is also added to detail why we are returning the value of the
parent cache and ignoring the children's when we propagate the attributes.
Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/memcontrol.h | 6 ++++++
mm/slab.c | 1 +
mm/slub.c | 21 +++++++++++++++++----
3 files changed, 24 insertions(+), 4 deletions(-)
diff -puN include/linux/memcontrol.h~memcg-add-comments-clarifying-aspects-of-cache-attribute-propagation include/linux/memcontrol.h
--- a/include/linux/memcontrol.h~memcg-add-comments-clarifying-aspects-of-cache-attribute-propagation
+++ a/include/linux/memcontrol.h
@@ -415,6 +415,12 @@ static inline void sock_release_memcg(st
extern struct static_key memcg_kmem_enabled_key;
extern int memcg_limited_groups_array_size;
+
+/*
+ * Helper macro to loop through all memcg-specific caches. Callers must still
+ * check if the cache is valid (it is either valid or NULL).
+ * the slab_mutex must be held when looping through those caches
+ */
#define for_each_memcg_cache_index(_idx) \
for ((_idx) = 0; i < memcg_limited_groups_array_size; (_idx)++)
diff -puN mm/slab.c~memcg-add-comments-clarifying-aspects-of-cache-attribute-propagation mm/slab.c
--- a/mm/slab.c~memcg-add-comments-clarifying-aspects-of-cache-attribute-propagation
+++ a/mm/slab.c
@@ -4154,6 +4154,7 @@ static int do_tune_cpucache(struct kmem_
if ((ret < 0) || !is_root_cache(cachep))
return ret;
+ VM_BUG_ON(!mutex_is_locked(&slab_mutex));
for_each_memcg_cache_index(i) {
c = cache_from_memcg(cachep, i);
if (c)
diff -puN mm/slub.c~memcg-add-comments-clarifying-aspects-of-cache-attribute-propagation mm/slub.c
--- a/mm/slub.c~memcg-add-comments-clarifying-aspects-of-cache-attribute-propagation
+++ a/mm/slub.c
@@ -5191,12 +5191,25 @@ static ssize_t slab_attr_store(struct ko
if (s->max_attr_size < len)
s->max_attr_size = len;
+ /*
+ * This is a best effort propagation, so this function's return
+ * value will be determined by the parent cache only. This is
+ * basically because not all attributes will have a well
+ * defined semantics for rollbacks - most of the actions will
+ * have permanent effects.
+ *
+ * Returning the error value of any of the children that fail
+ * is not 100 % defined, in the sense that users seeing the
+ * error code won't be able to know anything about the state of
+ * the cache.
+ *
+ * Only returning the error code for the parent cache at least
+ * has well defined semantics. The cache being written to
+ * directly either failed or succeeded, in which case we loop
+ * through the descendants with best-effort propagation.
+ */
for_each_memcg_cache_index(i) {
struct kmem_cache *c = cache_from_memcg(s, i);
- /*
- * This function's return value is determined by the
- * parent cache only
- */
if (c)
attribute->store(c, buf, len);
}
_
Patches currently in -mm which might be from glommer@xxxxxxxxxxxxx are
linux-next.patch
memcg-make-it-possible-to-use-the-stock-for-more-than-one-page.patch
memcg-reclaim-when-more-than-one-page-needed.patch
memcg-change-defines-to-an-enum.patch
memcg-kmem-accounting-basic-infrastructure.patch
mm-add-a-__gfp_kmemcg-flag.patch
memcg-kmem-controller-infrastructure.patch
memcg-kmem-controller-infrastructure-replace-__always_inline-with-plain-inline.patch
mm-allocate-kernel-pages-to-the-right-memcg.patch
res_counter-return-amount-of-charges-after-res_counter_uncharge.patch
memcg-kmem-accounting-lifecycle-management.patch
memcg-use-static-branches-when-code-not-in-use.patch
memcg-allow-a-memcg-with-kmem-charges-to-be-destructed.patch
memcg-execute-the-whole-memcg-freeing-in-free_worker.patch
fork-protect-architectures-where-thread_size-=-page_size-against-fork-bombs.patch
memcg-add-documentation-about-the-kmem-controller.patch
slab-slub-struct-memcg_params.patch
slab-annotate-on-slab-caches-nodelist-locks.patch
slab-slub-consider-a-memcg-parameter-in-kmem_create_cache.patch
memcg-allocate-memory-for-memcg-caches-whenever-a-new-memcg-appears.patch
memcg-allocate-memory-for-memcg-caches-whenever-a-new-memcg-appears-simplify-ida-initialization.patch
memcg-infrastructure-to-match-an-allocation-to-the-right-cache.patch
memcg-skip-memcg-kmem-allocations-in-specified-code-regions.patch
memcg-skip-memcg-kmem-allocations-in-specified-code-regions-remove-test-for-current-mm-in-memcg_stop-resume_kmem_account.patch
slb-always-get-the-cache-from-its-page-in-kmem_cache_free.patch
slb-allocate-objects-from-memcg-cache.patch
memcg-destroy-memcg-caches.patch
memcg-destroy-memcg-caches-move-include-of-workqueueh-to-top-of-slabh-file.patch
memcg-slb-track-all-the-memcg-children-of-a-kmem_cache.patch
memcg-slb-shrink-dead-caches.patch
memcg-slb-shrink-dead-caches-get-rid-of-once-per-second-cache-shrinking-for-dead-memcgs.patch
memcg-aggregate-memcg-cache-values-in-slabinfo.patch
slab-propagate-tunable-values.patch
slub-slub-specific-propagation-changes.patch
slub-slub-specific-propagation-changes-fix.patch
kmem-add-slab-specific-documentation-about-the-kmem-controller.patch
memcg-add-comments-clarifying-aspects-of-cache-attribute-propagation.patch
slub-drop-mutex-before-deleting-sysfs-entry.patch
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