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Date: Wed, 9 Dec 2015 13:41:07 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
Subject: Re: [RFC PATCH V2 8/9] slab: implement bulk free in SLAB allocator
In-Reply-To: <20151209195325.68eaf314@redhat.com>
Message-ID: <alpine.DEB.2.20.1512091338240.7552@east.gentwo.org>
References: <20151208161751.21945.53936.stgit@firesoul> <20151208161903.21945.33876.stgit@firesoul> <alpine.DEB.2.20.1512090945570.30894@east.gentwo.org> <20151209195325.68eaf314@redhat.com>
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Sender: owner-linux-mm@kvack.org
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To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: linux-mm@kvack.org, Vladimir Davydov <vdavydov@virtuozzo.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>

On Wed, 9 Dec 2015, Jesper Dangaard Brouer wrote:

> I really like the idea of making it able to free kmalloc'ed objects.
> But I hate to change the API again... (I do have a use-case in the
> network stack where I could use this feature).

Now is the time to fix the API since its not that much in use yet if at
all.

> I'm traveling (to Sweden) Thursday (afternoon) and will be back late
> Friday (and have to play Viking in the weekend), thus to be realistic
> I'll start working on this Monday, so we can get some benchmark numbers
> to guide this decision.

Ok great.
> > -		struct kmem_cache *s;
> > +		struct page *page;
> >
> > -		/* Support for memcg */
> > -		s = cache_from_obj(orig_s, p[size - 1]);
> > +		page = virt_to_head_page(p[size - 1]);
>
> Think we can drop this.

Well then you wont be able to check for a compound page. And you do not
want this check in build detached freelist.

>
> > -		size = build_detached_freelist(s, size, p, &df);
> > +		if (unlikely(!PageSlab(page))) {
> > +			BUG_ON(!PageCompound(page));
> > +			kfree_hook(p[size - 1]);
> > +			__free_kmem_pages(page, compound_order(page));
> > +			p[--size] = NULL;
> > +			continue;
> > +		}
>
> and move above into build_detached_freelist() and make it a little more
> pretty code wise (avoiding the p[size -1] juggling).

If we do this check here then we wont be needing it in
build_detached_freelist.

> > +
> > +		size = build_detached_freelist(page->slab_cache, size, p, &df);
>
> also think we should be able to drop the kmem_cache param "page->slab_cache".

Yep.

>
>
> >  		if (unlikely(!df.page))
> >  			continue;
> >
> > -		slab_free(s, df.page, df.freelist, df.tail, df.cnt, _RET_IP_);
> > +		slab_free(page->slab_cache, df.page, df.freelist, df.tail, df.cnt, _RET_IP_);

Then we need df.slab_cache or something.

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