From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f179.google.com (mail-pd0-f179.google.com [209.85.192.179]) by kanga.kvack.org (Postfix) with ESMTP id 5C7736B0035 for ; Fri, 10 Jan 2014 05:20:41 -0500 (EST) Received: by mail-pd0-f179.google.com with SMTP id y13so1894507pdi.10 for ; Fri, 10 Jan 2014 02:20:41 -0800 (PST) Received: from e23smtp01.au.ibm.com (e23smtp01.au.ibm.com. [202.81.31.143]) by mx.google.com with ESMTPS id e8si6695197pac.53.2014.01.10.02.20.38 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Fri, 10 Jan 2014 02:20:40 -0800 (PST) Received: from /spool/local by e23smtp01.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 10 Jan 2014 20:20:36 +1000 Received: from d23relay05.au.ibm.com (d23relay05.au.ibm.com [9.190.235.152]) by d23dlp02.au.ibm.com (Postfix) with ESMTP id 4EB6B2BB0053 for ; Fri, 10 Jan 2014 21:20:34 +1100 (EST) Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139]) by d23relay05.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s0AA1YXI2490824 for ; Fri, 10 Jan 2014 21:01:36 +1100 Received: from d23av04.au.ibm.com (localhost [127.0.0.1]) by d23av04.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s0AAKV9s004727 for ; Fri, 10 Jan 2014 21:20:31 +1100 Message-ID: <52CFCB2D.7080104@linux.vnet.ibm.com> Date: Fri, 10 Jan 2014 15:57:57 +0530 From: Raghavendra K T MIME-Version: 1.0 Subject: Re: [RFC PATCH V4] mm readahead: Fix readahead fail for no local memory and limit readahead pages References: <1389295490-28707-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com> <20140110083656.GC26378@quack.suse.cz> <20140110095222.GE26378@quack.suse.cz> In-Reply-To: <20140110095222.GE26378@quack.suse.cz> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Jan Kara , Andrew Morton , Linus Cc: Fengguang Wu , David Cohen , Al Viro , Damien Ramonda , linux-mm@kvack.org, linux-kernel@vger.kernel.org On 01/10/2014 03:22 PM, Jan Kara wrote: > On Fri 10-01-14 09:36:56, Jan Kara wrote: >> On Fri 10-01-14 00:54:50, Raghavendra K T wrote: >>> We limit the number of readahead pages to 4k. >>> >>> max_sane_readahead returns zero on the cpu having no local memory >>> node. Fix that by returning a sanitized number of pages viz., >>> minimum of (requested pages, 4k, number of local free pages) >>> >>> Result: >>> fadvise experiment with FADV_WILLNEED on a x240 machine with 1GB testfile >>> 32GB* 4G RAM numa machine ( 12 iterations) yielded >>> >>> kernel Avg Stddev >>> base 7.264 0.56% >>> patched 7.285 1.14% >> OK, looks good to me. You can add: >> Reviewed-by: Jan Kara > Hum, while doing some other work I've realized there may be still a > problem hiding with the 16 MB limitation. E.g. the dynamic linker is > doing MADV_WILLNEED on the shared libraries. If the library (or executable) > is larger than 16 MB, then it may cause performance problems since access > is random in nature and we don't really know which part of the file do we > need first. > > I'm not sure what others think about this but I'm now more inclined to a > bit more careful and introduce the 16 MB limit only for the NUMA case. I.e. > something like: Your suggestion makes sense. I do not have any strong preference. may be we shall wait for Linus/Andrew's comments (if any) since Linus suggested the 16MB idea. > > unsigned long local_free_page; > int nid; > > nid = numa_node_id(); > if (node_present_pages(nid)) { > /* > * We sanitize readahead size depending on free memory in > * the local node. > */ > local_free_page = node_page_state(nid, NR_INACTIVE_FILE) > + node_page_state(nid, NR_FREE_PAGES); > return min(nr, local_free_page / 2); > } > /* > * Readahead onto remote memory is better than no readahead when local > * numa node does not have memory. We limit the readahead to 4k > * pages though to avoid trashing page cache. > */ > return min(nr, MAX_REMOTE_READAHEAD); > -- 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