From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 615B66B025F for ; Wed, 16 Aug 2017 13:20:15 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id d5so18991235pfg.3 for ; Wed, 16 Aug 2017 10:20:15 -0700 (PDT) Received: from mailout3.samsung.com (mailout3.samsung.com. [203.254.224.33]) by mx.google.com with ESMTPS id a15si784034pfl.347.2017.08.16.10.20.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 16 Aug 2017 10:20:13 -0700 (PDT) Received: from epcas5p2.samsung.com (unknown [182.195.41.40]) by mailout3.samsung.com (KnoxPortal) with ESMTP id 20170816172011epoutp037ea267e1cdd5bba2e4dd6ae72a977ff5~bYzw-QPf42221422214epoutp03M for ; Wed, 16 Aug 2017 17:20:11 +0000 (GMT) Mime-Version: 1.0 Subject: [PATCH v2] zswap: Zero-filled pages handling Reply-To: srividya.dr@samsung.com From: Srividya Desireddy Message-ID: <20170816172008epcms5p24e951e01951f055559210af10edf2250@epcms5p2> Date: Wed, 16 Aug 2017 17:20:08 +0000 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" References: Sender: owner-linux-mm@kvack.org List-ID: To: "ddstreet@ieee.org" , "sergey.senozhatsky.work@gmail.com" , "sjenning@redhat.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "penberg@kernel.org" , Dinakar Reddy Pathireddy , SHARAN ALLUR , JUHUN KIM , "srividya.desireddy@gmail.com" , Sarbojit Ganguly On Thu, Jul 6, 2017 at 3:32 PM, Dan Streetman wrote: > On Thu, Jul 6, 2017 at 5:29 AM, Srividya Desireddy > wrote: >> On Wed, Jul 6, 2017 at 10:49 AM, Sergey Senozhatsky wrote: >>> On (07/02/17 20:28), Seth Jennings wrote: >>>> On Sun, Jul 2, 2017 at 9:19 AM, Srividya Desireddy >>>> > Zswap is a cache which compresses the pages that are being swapped out >>>> > and stores them into a dynamically allocated RAM-based memory pool. >>>> > Experiments have shown that around 10-20% of pages stored in zswap >>>> > are zero-filled pages (i.e. contents of the page are all zeros), but >>>> > these pages are handled as normal pages by compressing and allocating >>>> > memory in the pool. >>>> >>>> I am somewhat surprised that this many anon pages are zero filled. >>>> >>>> If this is true, then maybe we should consider solving this at the >>>> swap level in general, as we can de-dup zero pages in all swap >>>> devices, not just zswap. >>>> >>>> That being said, this is a fair small change and I don't see anything >>>> objectionable. However, I do think the better solution would be to do >>> this at a higher level. >>> >> >> Thank you for your suggestion. It is a better solution to handle >> zero-filled pages before swapping-out to zswap. Since, Zram is already >> handles Zero pages internally, I considered to handle within Zswap. >> In a long run, we can work on it to commonly handle zero-filled anon >> pages. >> >>> zero-filled pages are just 1 case. in general, it's better >>> to handle pages that are memset-ed with the same value (e.g. >>> memset(page, 0x01, page_size)). which includes, but not >>> limited to, 0x00. zram does it. >>> >>> -ss >> >> It is a good solution to extend zero-filled pages handling to same value >> pages. I will work on to identify the percentage of same value pages >> excluding zero-filled pages in Zswap and will get back. > > Yes, this sounds like a good modification to the patch. Also, unless > anyone else disagrees, it may be good to control this with a module > param - in case anyone has a use case that they know won't be helped > by this, and the extra overhead of checking each page is wasteful. > Probably should default to enabled. > >> >> - Srividya I have made changes to patch to handle pages with same-value filled. I tested on a ARM Quad Core 32-bit device with 1.5GB RAM by launching and relaunching different applications. After the test, out of ~64000 pages stored in zswap, ~ 11000 pages were same-value filled pages (including zero-filled pages) and ~9000 pages were zero-filled pages. An average of 17% of pages(including zero-filled pages) in zswap are same-value filled pages and 14% pages are zero-filled pages. An average of 3% of pages are same-filled non-zero pages. The below table shows the execution time profiling with the patch. Baseline With patch % Improvement ----------------------------------------------------------------- *Zswap Store Time 26.5ms 18ms 32% (of same value pages) *Zswap Load Time (of same value pages) 25.5ms 13ms 49% ----------------------------------------------------------------- On Ubuntu PC with 2GB RAM, while executing kernel build and other test scripts and running multimedia applications, out of 360000 pages stored in zswap 78000(~22%) of pages were found to be same-value filled pages (including zero-filled pages) and 64000(~17%) are zero-filled pages. So an average of %5 of pages are same-filled non-zero pages. The below table shows the execution time profiling with the patch. Baseline With patch % Improvement ----------------------------------------------------------------- *Zswap Store Time 91ms 74ms 19% (of same value pages) *Zswap Load Time 50ms 7.5ms 85% (of same value pages) ----------------------------------------------------------------- *The execution times may vary with test device used. I will send this patch of handling same-value filled pages along with module param to control it(default being enabled). - Srividya -- 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