Re: [PATCH v2 16/17] mm/slab: introduce new slab management type, OBJFREELIST_SLAB
From: Christoph Lameter
Date: Fri Feb 26 2016 - 11:21:30 EST
On Fri, 26 Feb 2016, js1304@xxxxxxxxx wrote:
> Although this idea can apply to all caches whose size is larger than
> management array size, it isn't applied to caches which have a
> constructor. If such cache's object is used for management array,
> constructor should be called for it before that object is returned to
> user. I guess that overhead overwhelm benefit in that case so this idea
> doesn't applied to them at least now.
Caches which have a constructor (or are used with SLAB_RCU_FREE) have a
defined content even when they are free. Therefore they cannot be used
for the freelist.
> For summary, from now on, slab management type is determined by
> following logic.
> 1) if management array size is smaller than object size and no ctor, it
> becomes OBJFREELIST_SLAB.
Also do not do this for RCU slabs.
> 2) if management array size is smaller than leftover, it becomes
> NORMAL_SLAB which uses leftover as a array.
> 3) if OFF_SLAB help to save memory than way 4), it becomes OFF_SLAB.
> It allocate a management array from the other cache so memory waste
Wonder how many of these ugly off slabs are left after what you did here.
> TOTAL = OBJFREELIST + NORMAL(leftover) + NORMAL + OFF
> 126 = 0 + 60 + 25 + 41
> 126 = 97 + 12 + 15 + 2
> Result shows that number of caches that doesn't waste memory increase
> from 60 to 109.
> v2: fix SLAB_DESTROTY_BY_RCU cache type handling
Ok how are they handled now? Do not see that dealt with in the patch.