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 19:06:24 -0400 |
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On 5/5/21 6:19 PM, Roman Gushchin wrote: > On Wed, May 05, 2021 at 11:29:54PM +0200, Vlastimil Babka wrote: >> On 5/5/21 8:32 PM, Roman Gushchin wrote: >>> On Wed, May 05, 2021 at 08:02:06PM +0200, 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 */ >>> Wait, s->refcount is adjusted to 1 in create_kmalloc_cache() after calling >>> into create_boot_cache? >> Hmm I missed that >> >> Now I wonder why all kmalloc caches on my system have 0 aliases :) >> cat /sys/kernel/slab/kmalloc-*/aliases > Yeah, I noticed it too, it's a good question. And I remember a case from > the past when it wasn't true (kmalloc-32 was shared with something else). > The criteria for cache merging require close to exact match in all attributes with a size difference of no more than sizeof(void *). So it is not easy to find a close match.
Cheers, Longman
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