Messages in this thread | | | From | Waiman Long <> | Subject | Re: [PATCH v3 2/2] mm: memcg/slab: Create a new set of kmalloc-cg-<n> caches | Date | Wed, 5 May 2021 14:31:28 -0400 |
| |
On 5/5/21 2:02 PM, Vlastimil Babka wrote: > On 5/5/21 7:30 PM, Roman Gushchin wrote: >> On Wed, May 05, 2021 at 11:46:13AM -0400, Waiman Long wrote: >>> With this change, all the objcg pointer array objects will come from >>> KMALLOC_NORMAL caches which won't have their objcg pointer arrays. So >>> both the recursive kfree() problem and non-freeable slab problem are >>> gone. Since both the KMALLOC_NORMAL and KMALLOC_CGROUP caches no longer >>> have mixed accounted and unaccounted objects, this will slightly reduce >>> the number of objcg pointer arrays that need to be allocated and save >>> a bit of memory. >> Unfortunately the positive effect of this change will be likely >> reversed by a lower utilization due to a larger number of caches. >> >> Btw, I wonder if we also need a change in the slab caches merging procedure? >> KMALLOC_NORMAL caches should not be merged with caches which can potentially >> include accounted objects. > Good point. But looks like kmalloc* caches are extempt from all merging in > create_boot_cache() via > > s->refcount = -1; /* Exempt from merging for now */ > > It wouldn't hurt though to create the kmalloc-cg-* caches with SLAB_ACCOUNT flag > to prevent accidental merging in case the above is ever removed. It would also > better reflect reality, and ensure that the array is allocated immediately with > the page, AFAICS. > I am not sure if this is really true.
struct kmem_cache *__init create_kmalloc_cache(const char *name, unsigned int size, slab_flags_t flags, unsigned int useroffset, unsigned int usersize) { struct kmem_cache *s = kmem_cache_zalloc(kmem_cache, GFP_NOWAIT);
if (!s) panic("Out of memory when creating slab %s\n", name);
create_boot_cache(s, name, size, flags, useroffset, usersize); kasan_cache_create_kmalloc(s); list_add(&s->list, &slab_caches); s->refcount = 1; return s; }
Even though refcount is set to -1 initially, it is set back to 1 afterward. So merging can still happen AFAICS.
Cheers, Longman
| |