From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D391CC77B7E for ; Thu, 25 May 2023 19:59:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242077AbjEYT7K (ORCPT ); Thu, 25 May 2023 15:59:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48612 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242078AbjEYT7G (ORCPT ); Thu, 25 May 2023 15:59:06 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AFCF790 for ; Thu, 25 May 2023 12:59:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=RwpqfGGYax+pT0MfFhzfIhAN71y4/MDvl/Gv7NEcip0=; b=oLpgFZXKkrtYOWRAbCHp7PQRav lquzf2zcJ26RmpzS5UFAL8NT3JPGzYq63xAMI1M3GfGZ9i1WH1t904bDMUDPQVQu/riz1mhMNWERz TOgqASQ+QbDvnsuNvwinwMCLYKtZgxFcO6cnRurXhmjrtmCPWcU8eJtgQ/6Sb+vq63l8qdIsLH8QG hY4ZTHrcleIeQTeMQvBgjt+i1xe7UPfmm5ZMlQkhpATEBiHF91EoNbRUEclX5uA/P6kGg9AUeH7E7 1i5doJchK0ufkm2guGo/zW81XeC2GjBZnpMq47JHJ3srZ5AhsAmc1G3F4BJXnC4q4Qp5xuISpjNxo lYgqBbEA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1q2H6k-00CVtH-EG; Thu, 25 May 2023 19:58:46 +0000 Date: Thu, 25 May 2023 20:58:46 +0100 From: Matthew Wilcox To: Khalid Aziz Cc: akpm@linux-foundation.org, steven.sistare@oracle.com, david@redhat.com, ying.huang@intel.com, mgorman@techsingularity.net, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Khalid Aziz Subject: Re: [PATCH v4] mm, compaction: Skip all non-migratable pages during scan Message-ID: References: <20230525191507.160076-1-khalid.aziz@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230525191507.160076-1-khalid.aziz@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 25, 2023 at 01:15:07PM -0600, Khalid Aziz wrote: > diff --git a/mm/compaction.c b/mm/compaction.c > index 5a9501e0ae01..b548e05f0349 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -764,6 +764,42 @@ static bool too_many_isolated(pg_data_t *pgdat) > return too_many; > } > > +/* > + * Check if this base page should be skipped from isolation because > + * it has extra refcounts that will prevent it from being migrated. > + * This code is inspired by similar code in migrate_vma_check_page(), > + * can_split_folio() and folio_migrate_mapping() > + */ > +static inline bool page_has_extra_refs(struct page *page, > + struct address_space *mapping) > +{ > + unsigned long extra_refs; > + struct folio *folio; > + > + /* > + * Skip this check for pages in ZONE_MOVABLE or MIGRATE_CMA > + * pages that can not be long term pinned > + */ > + if (is_zone_movable_page(page) || is_migrate_cma_page(page)) > + return false; > + > + folio = page_folio(page); > + > + /* > + * caller holds a ref already from get_page_unless_zero() > + * which is accounted for in folio_expected_refs() > + */ > + extra_refs = folio_expected_refs(mapping, folio); > + > + /* > + * This is an admittedly racy check but good enough to determine > + * if a page is pinned and can not be migrated > + */ > + if ((folio_ref_count(folio) - extra_refs) > folio_mapcount(folio)) > + return true; > + return false; > +} > + > /** > * isolate_migratepages_block() - isolate all migrate-able pages within > * a single pageblock > @@ -992,12 +1028,12 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > goto isolate_fail; Just out of shot, we have ... if (unlikely(!get_page_unless_zero(page))) This is the perfect opportunity to use folio_get_nontail_page() instead. You get back the folio without having to cast the pointer yourself or call page_folio(). Now you can use a folio throughout your new function, saving a call to compound_head(). For a followup patch, everything in this loop below this point can use the folio ... that's quite a lot of change. > /* > - * Migration will fail if an anonymous page is pinned in memory, > - * so avoid taking lru_lock and isolating it unnecessarily in an > - * admittedly racy check. > + * Migration will fail if a page has extra refcounts > + * from long term pinning preventing it from migrating, > + * so avoid taking lru_lock and isolating it unnecessarily. > */ Isn't "long term pinning" the wrong description of the problem? Long term pins suggest to me FOLL_LONGTERM. I think this is simple short term pins that we care about here.