On 04/17/2018 07:26 PM, Mikulas Patocka wrote: > > > On Tue, 17 Apr 2018, Vlastimil Babka wrote: > >> On 04/17/2018 04:45 PM, Christopher Lameter wrote: >>> On Mon, 16 Apr 2018, Mikulas Patocka wrote: >>> >>>> This patch introduces a flag SLAB_MINIMIZE_WASTE for slab and slub. This >>>> flag causes allocation of larger slab caches in order to minimize wasted >>>> space. >>>> >>>> This is needed because we want to use dm-bufio for deduplication index and >>>> there are existing installations with non-power-of-two block sizes (such >>>> as 640KB). The performance of the whole solution depends on efficient >>>> memory use, so we must waste as little memory as possible. >>> >>> Hmmm. Can we come up with a generic solution instead? >> >> Yes please. >> >>> This may mean relaxing the enforcement of the allocation max order a bit >>> so that we can get dense allocation through higher order allocs. >>> >>> But then higher order allocs are generally seen as problematic. >> >> I think in this case they are better than wasting/fragmenting 384kB for >> 640kB object. > > Wasting 37% of memory is still better than the kernel randomly returning > -ENOMEM when higher-order allocation fails. Of course, see below. >>> That >>> means that callers need to be able to tolerate failures. >> >> Is it any different from now? I suppose there would still be >> smallest-order fallback involved in sl*b itself? And if your allocation ^ There: "I suppose there would still be smallest-order fallback involved in sl*b itself?" If SLAB doesn't currently support fallback to different order, it either learns to do that, or keeps wasting memory and more people will migrate to SLUB. Simple.
