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 8DFC0C433EF for ; Thu, 19 May 2022 10:57:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237030AbiESK5I (ORCPT ); Thu, 19 May 2022 06:57:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41098 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229498AbiESK5E (ORCPT ); Thu, 19 May 2022 06:57:04 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5065C674C8 for ; Thu, 19 May 2022 03:57:03 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id EACE41F86A; Thu, 19 May 2022 10:57:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1652957821; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=8uZD/sZperneDqTPmd/3WdovVji6ii5Xr/81SKEuRI4=; b=SPinQL3l1IrJeHOkOXoaUvW+T4FUNTVr5LsgEoOKh0t0ydiKxpj3mAwY8bV0lpIdi8E+th TxHLIrqz+O4LOnz4G+2x2BE5dpXSD06fCKEmxH/Qkgskm2rY50xwQXAwj76VWu8rJpnSOE iUijMuYueXfTDri4cKSeUZGCOFZTBqQ= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1652957821; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=8uZD/sZperneDqTPmd/3WdovVji6ii5Xr/81SKEuRI4=; b=GFdxz3drPlEthQn5HQPEQgVP6OBYVfm5b3mhjwrdQffvVzpeuqVG+jYkjDFiozZEwVethz qAmY/KHBJIMBDpDw== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id C1C3913AF8; Thu, 19 May 2022 10:57:01 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id Q/E6Ln0ihmJdWwAAMHmgww (envelope-from ); Thu, 19 May 2022 10:57:01 +0000 Message-ID: <5a0c9b7c-3620-3e0f-7510-d0fc3fa6ceda@suse.cz> Date: Thu, 19 May 2022 12:57:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH 4/6] mm/page_alloc: Remove unnecessary page == NULL check in rmqueue Content-Language: en-US To: Mel Gorman , Andrew Morton Cc: Nicolas Saenz Julienne , Marcelo Tosatti , Michal Hocko , LKML , Linux-MM References: <20220512085043.5234-1-mgorman@techsingularity.net> <20220512085043.5234-5-mgorman@techsingularity.net> From: Vlastimil Babka In-Reply-To: <20220512085043.5234-5-mgorman@techsingularity.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/12/22 10:50, Mel Gorman wrote: > The VM_BUG_ON check for a valid page can be avoided with a simple > change in the flow. The ZONE_BOOSTED_WATERMARK is unlikely in general > and even more unlikely if the page allocation failed so mark the > branch unlikely. Hm, so that makes a DEBUG_VM config avoid the check. On the other hand, it puts it on the path returning from rmqueue_pcplist() for all configs, and that should be the fast path. So unless things further change in the following patches, it doesn't seem that useful? > Signed-off-by: Mel Gorman > Tested-by: Minchan Kim > Acked-by: Minchan Kim > --- > mm/page_alloc.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 1c4c54503a5d..b543333dce8f 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3765,17 +3765,18 @@ struct page *rmqueue(struct zone *preferred_zone, > > page = rmqueue_buddy(preferred_zone, zone, order, alloc_flags, > migratetype); > - if (unlikely(!page)) > - return NULL; > > out: > /* Separate test+clear to avoid unnecessary atomics */ > - if (test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags)) { > + if (unlikely(test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags))) { > clear_bit(ZONE_BOOSTED_WATERMARK, &zone->flags); > wakeup_kswapd(zone, 0, 0, zone_idx(zone)); > } > > - VM_BUG_ON_PAGE(page && bad_range(zone, page), page); > + if (unlikely(!page)) > + return NULL; > + > + VM_BUG_ON_PAGE(bad_range(zone, page), page); > return page; > } >