From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx195.postini.com [74.125.245.195]) by kanga.kvack.org (Postfix) with SMTP id 55AF76B003B for ; Wed, 10 Apr 2013 21:55:24 -0400 (EDT) Received: by mail-ia0-f175.google.com with SMTP id e16so991435iaa.34 for ; Wed, 10 Apr 2013 18:55:23 -0700 (PDT) Date: Wed, 10 Apr 2013 20:55:19 -0500 From: Rob Landley Subject: Re: [PATCHv9 2/8] zsmalloc: add documentation In-Reply-To: <1365617940-21623-3-git-send-email-sjenning@linux.vnet.ibm.com> (from sjenning@linux.vnet.ibm.com on Wed Apr 10 13:18:54 2013) Message-Id: <1365645319.18069.73@driftwood> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; DelSp=Yes; Format=Flowed Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Seth Jennings Cc: Andrew Morton , Greg Kroah-Hartman , Nitin Gupta , Minchan Kim , Konrad Rzeszutek Wilk , Dan Magenheimer , Robert Jennings , Jenifer Hopper , Mel Gorman , Johannes Weiner , Rik van Riel , Larry Woodman , Benjamin Herrenschmidt , Dave Hansen , Joe Perches , Joonsoo Kim , Cody P Schafer , Hugh Dickens , Paul Mackerras , Heesub Shin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org On 04/10/2013 01:18:54 PM, Seth Jennings wrote: > This patch adds a documentation file for zsmalloc at > Documentation/vm/zsmalloc.txt Docs acked-by: Rob Landley Literary criticism below: > Signed-off-by: Seth Jennings > --- > Documentation/vm/zsmalloc.txt | 68 =20 > +++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 68 insertions(+) > create mode 100644 Documentation/vm/zsmalloc.txt >=20 > diff --git a/Documentation/vm/zsmalloc.txt =20 > b/Documentation/vm/zsmalloc.txt > new file mode 100644 > index 0000000..85aa617 > --- /dev/null > +++ b/Documentation/vm/zsmalloc.txt > @@ -0,0 +1,68 @@ > +zsmalloc Memory Allocator > + > +Overview > + > +zmalloc a new slab-based memory allocator, > +zsmalloc, for storing compressed pages. zmalloc a new slab-based memory allocator, zsmalloc? (How does one =20 zmalloc zsmalloc?) Out of curiosity, what does zsmalloc stand for, anyway? > It is designed for > +low fragmentation and high allocation success rate on > +large object, but <=3D PAGE_SIZE allocations. 1) objects 2) maybe "large objects for <=3D PAGE_SIZE"... > +zsmalloc differs from the kernel slab allocator in two primary > +ways to achieve these design goals. > + > +zsmalloc never requires high order page allocations to back > +slabs, or "size classes" in zsmalloc terms. Instead it allows > +multiple single-order pages to be stitched together into a > +"zspage" which backs the slab. This allows for higher allocation > +success rate under memory pressure. > + > +Also, zsmalloc allows objects to span page boundaries within the > +zspage. This allows for lower fragmentation than could be had > +with the kernel slab allocator for objects between PAGE_SIZE/2 > +and PAGE_SIZE. With the kernel slab allocator, if a page compresses > +to 60% of it original size, the memory savings gained through > +compression is lost in fragmentation because another object of I lean towards "are lost", but it's debatable. (Savings are plural, but =20 savings could also be treated as a mass noun like water/air/bison that =20 doesn't get pluralized because you can't count instances of a liquid. =20 No idea which is more common.) > +the same size can't be stored in the leftover space. > + > +This ability to span pages results in zsmalloc allocations not being > +directly addressable by the user. The user is given an > +non-dereferencable handle in response to an allocation request. > +That handle must be mapped, using zs_map_object(), which returns > +a pointer to the mapped region that can be used. The mapping is > +necessary since the object data may reside in two different > +noncontigious pages. Presumably this allows packing of unmapped entities if you detect =20 fragmentation and are up for a latency spike? Rob= -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org