Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753270AbbG2MZT (ORCPT ); Wed, 29 Jul 2015 08:25:19 -0400 Received: from mx2.suse.de ([195.135.220.15]:50183 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752917AbbG2MZR (ORCPT ); Wed, 29 Jul 2015 08:25:17 -0400 Subject: Re: [PATCH 10/10] mm, page_alloc: Only enforce watermarks for order-0 allocations To: Mel Gorman , Linux-MM References: <1437379219-9160-1-git-send-email-mgorman@suse.com> <1437379219-9160-11-git-send-email-mgorman@suse.com> Cc: Johannes Weiner , Rik van Riel , Pintu Kumar , Xishi Qiu , Gioh Kim , LKML , Mel Gorman From: Vlastimil Babka X-Enigmail-Draft-Status: N1110 Message-ID: <55B8C629.80303@suse.cz> Date: Wed, 29 Jul 2015 14:25:13 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.0.1 MIME-Version: 1.0 In-Reply-To: <1437379219-9160-11-git-send-email-mgorman@suse.com> Content-Type: text/plain; charset=iso-8859-2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2729 Lines: 80 On 07/20/2015 10:00 AM, Mel Gorman wrote: [...] > static bool __zone_watermark_ok(struct zone *z, unsigned int order, > unsigned long mark, int classzone_idx, int alloc_flags, > @@ -2259,7 +2261,7 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order, > { > long min = mark; > int o; > - long free_cma = 0; > + const bool atomic = (alloc_flags & ALLOC_HARDER); > > /* free_pages may go negative - that's OK */ > free_pages -= (1 << order) - 1; > @@ -2271,7 +2273,7 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order, > * If the caller is not atomic then discount the reserves. This will > * over-estimate how the atomic reserve but it avoids a search > */ > - if (likely(!(alloc_flags & ALLOC_HARDER))) > + if (likely(!atomic)) > free_pages -= z->nr_reserved_highatomic; > else > min -= min / 4; > @@ -2279,22 +2281,30 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order, > #ifdef CONFIG_CMA > /* If allocation can't use CMA areas don't use free CMA pages */ > if (!(alloc_flags & ALLOC_CMA)) > - free_cma = zone_page_state(z, NR_FREE_CMA_PAGES); > + free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES); > #endif > > - if (free_pages - free_cma <= min + z->lowmem_reserve[classzone_idx]) > + if (free_pages <= min + z->lowmem_reserve[classzone_idx]) > return false; > - for (o = 0; o < order; o++) { > - /* At the next order, this order's pages become unavailable */ > - free_pages -= z->free_area[o].nr_free << o; > > - /* Require fewer higher order pages to be free */ > - min >>= 1; > + /* order-0 watermarks are ok */ > + if (!order) > + return true; > + > + /* Check at least one high-order page is free */ > + for (o = order; o < MAX_ORDER; o++) { > + struct free_area *area = &z->free_area[o]; > + int mt; > + > + if (atomic && area->nr_free) > + return true; This may be a false positive due to MIGRATE_CMA or MIGRATE_ISOLATE pages being the only free ones. But maybe it doesn't matter that much? > > - if (free_pages <= min) > - return false; > + for (mt = 0; mt < MIGRATE_PCPTYPES; mt++) { > + if (!list_empty(&area->free_list[mt])) > + return true; > + } This may be a false negative for ALLOC_CMA allocations, if the only free pages are of MIGRATE_CMA. Arguably that's the worse case than a false positive? > } > - return true; > + return false; > } > > bool zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, > -- 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/