From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 4F23C6B026F for ; Mon, 5 Nov 2018 04:28:53 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id x1-v6so5025753eds.16 for ; Mon, 05 Nov 2018 01:28:53 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z30-v6si2203865edb.342.2018.11.05.01.28.51 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 05 Nov 2018 01:28:52 -0800 (PST) Date: Mon, 5 Nov 2018 10:28:51 +0100 From: Michal Hocko Subject: Re: [PATCH] mm, memory_hotplug: teach has_unmovable_pages about of LRU migrateable pages Message-ID: <20181105092851.GD4361@dhcp22.suse.cz> References: <20181101091055.GA15166@MiWiFi-R3L-srv> <20181102155528.20358-1-mhocko@kernel.org> <20181105002009.GF27491@MiWiFi-R3L-srv> <20181105091407.GB4361@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181105091407.GB4361@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Baoquan He Cc: Andrew Morton , linux-mm@kvack.org, LKML , Stable tree On Mon 05-11-18 10:14:07, Michal Hocko wrote: > Maybe we can add a retry for movable zone pages. Or something like this. Ugly as hell, no question about that. I also have to think about this some more to convince myself this will not result in an endless loop under some situations. diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 48ceda313332..342d66eca0f3 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -7779,12 +7779,16 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count, pfn = page_to_pfn(page); for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) { unsigned long check = pfn + iter; + unsigned long saved_flags; if (!pfn_valid_within(check)) continue; page = pfn_to_page(check); +retry: + saved_flags = READ_ONCE(page->flags); + if (PageReserved(page)) goto unmovable; @@ -7840,6 +7844,13 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count, page->mapping->a_ops->migratepage) continue; + /* + * We might race with the allocation of the page so retry + * if flags have changed. + */ + if (saved_flags != READ_ONCE(page->flags)) + goto retry; + /* * If there are RECLAIMABLE pages, we need to check * it. But now, memory offline itself doesn't call -- Michal Hocko SUSE Labs