From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f198.google.com (mail-qt0-f198.google.com [209.85.216.198]) by kanga.kvack.org (Postfix) with ESMTP id 1FE9B6B0253 for ; Tue, 26 Jul 2016 15:23:45 -0400 (EDT) Received: by mail-qt0-f198.google.com with SMTP id c52so38353570qte.2 for ; Tue, 26 Jul 2016 12:23:45 -0700 (PDT) Received: from mail-qt0-f180.google.com (mail-qt0-f180.google.com. [209.85.216.180]) by mx.google.com with ESMTPS id s5si541187ybf.337.2016.07.26.12.23.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Jul 2016 12:23:44 -0700 (PDT) Received: by mail-qt0-f180.google.com with SMTP id 52so16658316qtq.3 for ; Tue, 26 Jul 2016 12:23:44 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20160725134732.b21912c54ef1ffe820ccdbca@linux-foundation.org> References: <1469457565-22693-1-git-send-email-kwalker@redhat.com> <20160725134732.b21912c54ef1ffe820ccdbca@linux-foundation.org> From: Kyle Walker Date: Tue, 26 Jul 2016 15:23:42 -0400 Message-ID: Subject: Re: [PATCH] mm: Move readahead limit outside of readahead, and advisory syscalls Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko , Geliang Tang , Vlastimil Babka , Roman Gushchin , "Kirill A. Shutemov" , Linus Torvalds On Mon, Jul 25, 2016 at 4:47 PM, Andrew Morton wrote: > > Can this suffering be quantified please? > The observed suffering is primarily visible within an IBM Qradar installation. From a high level, the lower limit to the amount of advisory readahead pages results in a 3-5x increase in time necessary to complete an identical query within the application. Note, all of the below values are with Readahead configured to 64Kib. Baseline behaviour - Prior to: 600e19af ("mm: use only per-device readahead limit") 6d2be915 ("mm/readahead.c: fix readahead failure for memoryless NUMA nodes and limit readahead pages") Result: Qradar - Command: "username equals root" - 57.3s to complete search New performance - With: 600e19af ("mm: use only per-device readahead limit") 6d2be915 ("mm/readahead.c: fix readahead failure for memoryless NUMA nodes and limit readahead pages") Result: Qradar - "username equals root" query - 245.7s to complete search Proposed behaviour - With the proposed patch in place. Result: Qradar - "username equals root" query - 57s to complete search In narrowing the source of the performance deficit, it was observed that the amount of data loaded into pagecache via madvise was quite a bit lower following the noted commits. As simply reverting those lower limits were not accepted previously, the proposed alternative strategy seemed like the most beneficial path forwards. > > Linus probably has opinions ;) > I understand that changes to readahead that are very similar have been proposed quite a bit lately. If there are any changes or testing needed, I'm more than happy to tackle that. Thank you in advance! -- Kyle Walker -- 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