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 Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ 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 -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html