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5:29 AM Harry Yoo wrote: > > > > When a cache has high s->align value and s->object_size is not aligned > > to it, each object ends up with some unused space because of alignment. > > If this wasted space is big enough, we can use it to store the > > slabobj_ext metadata instead of wasting it. > > > > On my system, this happens with caches like kmem_cache, mm_struct, pid, > > task_struct, sighand_cache, xfs_inode, and others. > > > > To place the slabobj_ext metadata within each object, the existing > > slab_obj_ext() logic can still be used by setting: > > > > - slab->obj_exts = slab_address(slab) + s->red_left_zone + > > (slabobj_ext offset) > > - stride = s->size > > > > slab_obj_ext() doesn't need know where the metadata is stored, > > so this method works without adding extra overhead to slab_obj_ext(). > > > > A good example benefiting from this optimization is xfs_inode > > (object_size: 992, align: 64). To measure memory savings, 2 millions of > > files were created on XFS. > > > > [ MEMCG=y, MEM_ALLOC_PROFILING=n ] > > > > Before patch (creating 2M directories on xfs): > > Slab: 6693844 kB > > SReclaimable: 6016332 kB > > SUnreclaim: 677512 kB > > > > After patch (creating 2M directories on xfs): > > Slab: 6697572 kB > > SReclaimable: 6034744 kB > > SUnreclaim: 662828 kB (-14.3 MiB) > > > > Enjoy the memory savings! > > > > Suggested-by: Vlastimil Babka > > Signed-off-by: Harry Yoo > > --- > > @@ -2250,7 +2293,8 @@ static inline void free_slab_obj_exts(struct slab *slab) > > if (!obj_exts) > > return; > > > > - if (obj_exts_in_slab(slab->slab_cache, slab)) { > > + if (obj_exts_in_slab(slab->slab_cache, slab) || > > + obj_exts_in_object(slab->slab_cache)) { > Hi Suren, thanks for the comment. I should have replied earlier, sorry. > I think you need a check for obj_exts_in_object() inside > alloc_slab_obj_exts() to avoid allocating the vector. But slab_obj_exts() check before alloc_slab_obj_exts() should have returned nonzero if obj_exts_in_object() returns true? > > slab->obj_exts = 0; > > return; > > } -- Cheers, Harry / Hyeonggon