From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ea0-f176.google.com (mail-ea0-f176.google.com [209.85.215.176]) by kanga.kvack.org (Postfix) with ESMTP id A479B6B0031 for ; Mon, 6 Jan 2014 05:56:24 -0500 (EST) Received: by mail-ea0-f176.google.com with SMTP id h14so7696329eaj.21 for ; Mon, 06 Jan 2014 02:56:23 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id i1si83312567eev.5.2014.01.06.02.56.22 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Mon, 06 Jan 2014 02:56:22 -0800 (PST) Date: Mon, 6 Jan 2014 11:56:20 +0100 From: Jan Kara Subject: Re: [RFC PATCH V3] mm readahead: Fix the readahead fail in case of empty numa node Message-ID: <20140106105620.GC3312@quack.suse.cz> References: <1389003715-29733-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1389003715-29733-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Raghavendra K T Cc: Andrew Morton , Fengguang Wu , David Cohen , Al Viro , Damien Ramonda , jack@suse.cz, Linus , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Mon 06-01-14 15:51:55, Raghavendra K T wrote: > Currently, max_sane_readahead returns zero on the cpu with empty numa node, > fix this by checking for potential empty numa node case during calculation. > We also limit the number of readahead pages to 4k. > > Signed-off-by: Raghavendra K T > --- > The current patch limits the readahead into 4k pages (16MB was suggested > by Linus). and also handles the case of memoryless cpu issuing readahead > failures. We still do not consider [fm]advise() specific calculations > here. I have dropped the iterating over numa node to calculate free page > idea. I do not have much idea whether there is any impact on big > streaming apps.. Comments/suggestions ? As you say I would be also interested what impact this has on a streaming application. It should be rather easy to check - create 1 GB file, drop caches. Then measure how long does it take to open the file, call fadvise FADV_WILLNEED, read the whole file (for a kernel with and without your patch). Do several measurements so that we get some meaningful statistics. Resulting numbers can then be part of the changelog. Thanks! Honza > mm/readahead.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/mm/readahead.c b/mm/readahead.c > index 7cdbb44..be4d205 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -237,14 +237,25 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp, > return ret; > } > > +#define MAX_REMOTE_READAHEAD 4096UL > /* > * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a > * sensible upper limit. > */ > unsigned long max_sane_readahead(unsigned long nr) > { > - return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE_FILE) > - + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2); > + unsigned long local_free_page; > + unsigned long sane_nr = min(nr, MAX_REMOTE_READAHEAD); > + > + local_free_page = node_page_state(numa_node_id(), NR_INACTIVE_FILE) > + + node_page_state(numa_node_id(), NR_FREE_PAGES); > + > + /* > + * Readahead onto remote memory is better than no readahead when local > + * numa node does not have memory. We sanitize readahead size depending > + * on free memory in the local node but limiting to 4k pages. > + */ > + return local_free_page ? min(sane_nr, local_free_page / 2) : sane_nr; > } > > /* > -- > 1.7.11.7 > -- Jan Kara SUSE Labs, CR -- 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