From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx161.postini.com [74.125.245.161]) by kanga.kvack.org (Postfix) with SMTP id 75E0D6B006E for ; Thu, 7 Jun 2012 17:20:55 -0400 (EDT) MIME-Version: 1.0 Message-ID: <06bd08dd-b8b4-4c7d-b8f3-f74f6270e51b@default> Date: Thu, 7 Jun 2012 14:20:40 -0700 (PDT) From: Dan Magenheimer Subject: RE: [PATCH 2/2] zram: clean up handle References: <1338881031-19662-1-git-send-email-minchan@kernel.org> <1338881031-19662-2-git-send-email-minchan@kernel.org> <4FCEE4E0.6030707@vflare.org> <4FD015FE.7070906@kernel.org> <4FD11A3C.801@vflare.org> In-Reply-To: <4FD11A3C.801@vflare.org> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Nitin Gupta Cc: Minchan Kim , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Konrad Wilk , Seth Jennings > From: Nitin Gupta [mailto:ngupta@vflare.org] > > Nitin, can zsmalloc allow full page allocation by assigning > > an actual physical pageframe (which is what zram does now)? > > Or will it allocate PAGE_SIZE bytes which zsmalloc will allocate > > crossing a page boundary which, presumably, will have much worse > > impact on page allocator availability when these pages are > > "reclaimed" via your swap notify callback. >=20 > zsmalloc does not add any object headers, so when allocating PAGE_SIZE > you get a separate page from as if you did alloc_page(). So, it does not > span page boundaries. >=20 > > Though this may be rare across all workloads, it may turn out > > to be very common for certain workloads (e.g. if the workload > > has many dirty anonymous pages that are already compressed > > by userland). > > > > It may not be worth cleaning up the code if it causes > > performance issues with this case. > > > > And anyway can zsmalloc handle and identify to the caller pages > > that are both compressed and "native" (uncompressed)? It > > certainly has to handle both if you remove ZRAM_UNCOMPRESSED > > as compressing some pages actually results in more than > > PAGE_SIZE bytes. So you need to record somewhere that > > this "compressed page" is special and that must somehow > > be communicated to the caller of your "get" routine. > > > > (Just trying to save Minchan from removing all that code but > > then needing to add it back again.) >=20 > zsmalloc cannot identify compressed vs uncompressed pages. However, in > zram, we can tell if the page is uncompressed using table[i]->size which > is set to PAGE_SIZE for uncompressed pages. Pages that compress to > more than PAGE_SIZE (i.e. expand on compression) are stored > as-is/uncompressed and thus will have size field set to PAGE_SIZE. >=20 > Thus, we do not require ZRAM_UNCOMPRESSED flag when using zsmalloc for > both compressed and uncompressed pages. Good to know. Nice work in zsmalloc and zram! Dan -- 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