On 3/21/19 3:23 AM, Matthew Wilcox wrote: > On Wed, Mar 20, 2019 at 10:48:03PM +0100, Vlastimil Babka wrote: >> >> Well, looks like that's what happens. This is with SLAB, but the alignment >> calculations should be common: >> >> slabinfo - version: 2.1 >> # name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables <limit> <batchcount> <sharedfactor> : slabdata <active_slabs> <num_slabs> <sharedavail> >> kmalloc-96 2611 4896 128 32 1 : tunables 120 60 8 : slabdata 153 153 0 >> kmalloc-128 4798 5536 128 32 1 : tunables 120 60 8 : slabdata 173 173 0 > > Hmm. On my laptop, I see: > > kmalloc-96 28050 35364 96 42 1 : tunables 0 0 0 : slabdata 842 842 0 > > That'd take me from 842 * 4k pages to 1105 4k pages -- an extra megabyte of > memory. > > This is running Debian's 4.19 kernel: > > # CONFIG_SLAB is not set > CONFIG_SLUB=y Ah, you're right. SLAB creates kmalloc caches with: #ifndef ARCH_KMALLOC_FLAGS #define ARCH_KMALLOC_FLAGS SLAB_HWCACHE_ALIGN #endif create_kmalloc_caches(ARCH_KMALLOC_FLAGS); While SLUB just: create_kmalloc_caches(0); even though it uses SLAB_HWCACHE_ALIGN for kmem_cache_node and kmem_cache caches.
