On Wed, Mar 26 2014, Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> wrote:
> We don't track any random page allocation, so we shouldn't track kmalloc
> that falls back to the page allocator.
This seems like a change which will leads to confusing (and arguably
improper) kernel behavior. I prefer the behavior prior to this patch.
Before this change both of the following allocations are charged to
memcg (assuming kmem accounting is enabled):
a = kmalloc(KMALLOC_MAX_CACHE_SIZE, GFP_KERNEL)
b = kmalloc(KMALLOC_MAX_CACHE_SIZE + 1, GFP_KERNEL)
After this change only 'a' is charged; 'b' goes directly to page
allocator which no longer does accounting.
> Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Cc: Glauber Costa <glommer@xxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
> Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> ---
> include/linux/slab.h | 2 +-
> mm/memcontrol.c | 27 +--------------------------
> mm/slub.c | 4 ++--
> 3 files changed, 4 insertions(+), 29 deletions(-)
>
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 3dd389aa91c7..8a928ff71d93 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -363,7 +363,7 @@ kmalloc_order(size_t size, gfp_t flags, unsigned int order)
> {
> void *ret;
>
> - flags |= (__GFP_COMP | __GFP_KMEMCG);
> + flags |= __GFP_COMP;
> ret = (void *) __get_free_pages(flags, order);
> kmemleak_alloc(ret, size, 1, flags);
> return ret;
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b4b6aef562fa..81a162d01d4d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3528,35 +3528,10 @@ __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
>
> *_memcg = NULL;
>
> - /*
> - * Disabling accounting is only relevant for some specific memcg
> - * internal allocations. Therefore we would initially not have such
> - * check here, since direct calls to the page allocator that are marked
> - * with GFP_KMEMCG only happen outside memcg core. We are mostly
> - * concerned with cache allocations, and by having this test at
> - * memcg_kmem_get_cache, we are already able to relay the allocation to
> - * the root cache and bypass the memcg cache altogether.
> - *
> - * There is one exception, though: the SLUB allocator does not create
> - * large order caches, but rather service large kmallocs directly from
> - * the page allocator. Therefore, the following sequence when backed by
> - * the SLUB allocator:
> - *
> - * memcg_stop_kmem_account();
> - * kmalloc(<large_number>)
> - * memcg_resume_kmem_account();
> - *
> - * would effectively ignore the fact that we should skip accounting,
> - * since it will drive us directly to this function without passing
> - * through the cache selector memcg_kmem_get_cache. Such large
> - * allocations are extremely rare but can happen, for instance, for the
> - * cache arrays. We bring this test here.
> - */
> - if (!current->mm || current->memcg_kmem_skip_account)
> + if (!current->mm)
> return true;
>
> memcg = get_mem_cgroup_from_mm(current->mm);
> -
> if (!memcg_can_account_kmem(memcg)) {
> css_put(&memcg->css);
> return true;
> diff --git a/mm/slub.c b/mm/slub.c
> index 5e234f1f8853..c2e58a787443 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3325,7 +3325,7 @@ static void *kmalloc_large_node(size_t size, gfp_t flags, int node)
> struct page *page;
> void *ptr = NULL;
>
> - flags |= __GFP_COMP | __GFP_NOTRACK | __GFP_KMEMCG;
> + flags |= __GFP_COMP | __GFP_NOTRACK;
> page = alloc_pages_node(node, flags, get_order(size));
> if (page)
> ptr = page_address(page);
> @@ -3395,7 +3395,7 @@ void kfree(const void *x)
> if (unlikely(!PageSlab(page))) {
> BUG_ON(!PageCompound(page));
> kfree_hook(x);
> - __free_memcg_kmem_pages(page, compound_order(page));
> + __free_pages(page, compound_order(page));
> return;
> }
> slab_free(page->slab_cache, page, object, _RET_IP_);
> --
> 1.7.10.4
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