linux-kernel - Re: [RFC 1/3] Slab infrastructure for array operations

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150129074443.GA19607@js1304-P5Q-DELUXE>
Date:	Thu, 29 Jan 2015 16:44:43 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	akpm@...uxfoundation.org, LKML <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Pekka Enberg <penberg@...nel.org>, iamjoonsoo@....com,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [RFC 1/3] Slab infrastructure for array operations

On Wed, Jan 28, 2015 at 09:30:56AM -0600, Christoph Lameter wrote:
> On Wed, 28 Jan 2015, Joonsoo Kim wrote:
> 
> > > GFP_SLAB_ARRAY new is best for large quantities in either allocator since
> > > SLAB also has to construct local metadata structures.
> >
> > In case of SLAB, there is just a little more work to construct local metadata so
> > GFP_SLAB_ARRAY_NEW would not show better performance
> > than GFP_SLAB_ARRAY_LOCAL, because it would cause more overhead due to
> > more page allocations. Because of this characteristic, I said that
> > which option is
> > the best is implementation specific and therefore we should not expose it.
> 
> For large amounts of objects (hundreds or higher) GFP_SLAB_ARRAY_LOCAL
> will never have enough objects. GFP_SLAB_ARRAY_NEW will go to the page
> allocator and bypass free table creation and all the queuing that objects
> go through normally in SLAB. AFAICT its going to be a significant win.
> 
> A similar situation is true for the freeing operation. If the freeing
> operation results in all objects in a page being freed then we can also
> bypass that and put the page directly back into the page allocator (to be
> implemented once we agree on an approach).
> 
> > Even if we narrow down the problem to the SLUB, choosing correct option is
> > difficult enough. User should know how many objects are cached in this
> > kmem_cache
> > in order to choose best option since relative quantity would make
> > performance difference.
> 
> Ok we can add a function call to calculate the number of objects cached
> per cpu and per node? But then that is rather fluid and could change any
> moment.
> 
> > And, how many objects are cached in this kmem_cache could be changed
> > whenever implementation changed.
> 
> The default when no options are specified is to first exhaust the node
> partial objects, then allocate new slabs as long as we have more than
> objects per page left and only then satisfy from cpu local object. I think
> that is satisfactory for the majority of the cases.
> 
> The detailed control options were requested at the meeting in Auckland at
> the LCA. I am fine with dropping those if they do not make sense. Makes
> the API and implementation simpler. Jesper, are you ok with this?

IMHO, it'd be better to choose a proper way of allocation by slab itself
and not to expose options to API user. We could decide the best option
according to current status of kmem_cache and requested object number
and internal implementation.

Is there any obvious example these option are needed for user?

Thanks.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/