Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754342AbaFDCUQ (ORCPT ); Tue, 3 Jun 2014 22:20:16 -0400 Received: from linuxhacker.ru ([217.76.32.60]:38033 "EHLO fiona.linuxhacker.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753963AbaFDCUK convert rfc822-to-8bit (ORCPT ); Tue, 3 Jun 2014 22:20:10 -0400 Subject: Re: [patch] mm, pcp: allow restoring percpu_pagelist_fraction default Mime-Version: 1.0 (Apple Message framework v1283) Content-Type: text/plain; charset=us-ascii From: Oleg Drokin In-Reply-To: Date: Tue, 3 Jun 2014 22:19:12 -0400 Cc: Andrew Morton , Rik van Riel , Mel Gorman , Cody P Schafer , Randy Dunlap , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, devel@driverdev.osuosl.org Content-Transfer-Encoding: 8BIT Message-Id: <85AFB547-D3A1-4818-AD82-FF90909775D2@linuxhacker.ru> References: <1399166883-514-1-git-send-email-green@linuxhacker.ru> <2C763027-307F-4BC0-8C0A-7E3D5957A4DA@linuxhacker.ru> To: David Rientjes X-Mailer: Apple Mail (2.1283) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello! On Jun 3, 2014, at 9:22 PM, David Rientjes wrote: > > @@ -5849,21 +5850,32 @@ int lowmem_reserve_ratio_sysctl_handler(ctl_table *table, int write, > int percpu_pagelist_fraction_sysctl_handler(ctl_table *table, int write, > void __user *buffer, size_t *length, loff_t *ppos) > { > + const int old_percpu_pagelist_fraction = percpu_pagelist_fraction; > struct zone *zone; > - unsigned int cpu; > int ret; > > ret = proc_dointvec_minmax(table, write, buffer, length, ppos); > - if (!write || (ret < 0)) > + if (!write || ret < 0) > return ret; > > + /* Sanity checking to avoid pcp imbalance */ > + if (percpu_pagelist_fraction && > + percpu_pagelist_fraction < MIN_PERCPU_PAGELIST_FRACTION) { > + percpu_pagelist_fraction = old_percpu_pagelist_fraction; > + return -EINVAL; > + } > + > + /* No change? */ > + if (percpu_pagelist_fraction == old_percpu_pagelist_fraction) > + return 0; > + > mutex_lock(&pcp_batch_high_lock); > for_each_populated_zone(zone) { > - unsigned long high; > - high = zone->managed_pages / percpu_pagelist_fraction; > + unsigned int cpu; > + > for_each_possible_cpu(cpu) > - pageset_set_high(per_cpu_ptr(zone->pageset, cpu), > - high); > + pageset_set_high_and_batch(zone, > + per_cpu_ptr(zone->pageset, cpu)); BTW, I just realized this version is racy (as was the previous one). A parallel writer could write a value of 0 while we are in the middle of pageset_set_high_and_batch and it's possible that'll result in division by zero still. Also it's possible an incorrect value might set for some of the zones. I imagine we might want to expand the lock area all the way up to before the proc_dointvec_minmax call jsut to be extra safe. > } > mutex_unlock(&pcp_batch_high_lock); > return 0; Bye, Oleg-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/