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 30784C38A2D for ; Tue, 25 Oct 2022 03:48:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229915AbiJYDsI (ORCPT ); Mon, 24 Oct 2022 23:48:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55752 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229535AbiJYDsD (ORCPT ); Mon, 24 Oct 2022 23:48:03 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A064D18E1F for ; Mon, 24 Oct 2022 20:48:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1666669681; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=PYgidL+/ri8mEQCVHJ40l8Y7OFSEYg6EaOK4xr7Faag=; b=ZbgzqJQi2mXpWCE8BIqnFDh/TRa4J9ZBxiUeoGIz5/QIHGKwIT101mp8skgvPi6FD2yAbu Qw/xEg2teJcbIEqC85A1kKyhNYZ+A8vcLS0H9Bf/Wh3vMXLZxHz+vb8tMdi1+MUIgEJDoC KUeRyvtg9aKFc8bSjuvEKyZnj9P5JAU= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-58-03pYwOQ6MRWC0gtGzitq9A-1; Mon, 24 Oct 2022 23:47:56 -0400 X-MC-Unique: 03pYwOQ6MRWC0gtGzitq9A-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id AFA241C05AFA; Tue, 25 Oct 2022 03:47:55 +0000 (UTC) Received: from localhost (ovpn-12-35.pek2.redhat.com [10.72.12.35]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0B474111F3B6; Tue, 25 Oct 2022 03:47:54 +0000 (UTC) Date: Tue, 25 Oct 2022 11:47:51 +0800 From: Baoquan He To: Dennis Zhou Cc: linux-kernel@vger.kernel.org, Tejun Heo , Christoph Lameter , Andrew Morton , linux-mm@kvack.org Subject: Re: [PATCH 4/8] mm/percpu: add comment to state the empty populated pages accounting Message-ID: References: <20221024081435.204970-1-bhe@redhat.com> <20221024081435.204970-5-bhe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/24/22 at 09:56am, Dennis Zhou wrote: > On Mon, Oct 24, 2022 at 04:14:31PM +0800, Baoquan He wrote: > > When allocating an area from a chunk, pcpu_block_update_hint_alloc() > > is called to update chunk metadata, including chunk's and global > > nr_empty_pop_pages. However, if the allocation is not atomic, some > > blocks may not be populated with pages yet, while we still account it > > here. The number of pages will be subtracted with pcpu_chunk_populated() > > when populating pages. > > > > Adding code comment to make that more understandable. > > > > Signed-off-by: Baoquan He > > --- > > mm/percpu.c | 14 +++++++++++--- > > 1 file changed, 11 insertions(+), 3 deletions(-) > > > > diff --git a/mm/percpu.c b/mm/percpu.c > > index a8121302a79c..09e407338573 100644 > > --- a/mm/percpu.c > > +++ b/mm/percpu.c > > @@ -831,13 +831,15 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off, > > > > /* > > * Update s_block. > > - * block->first_free must be updated if the allocation takes its place. > > - * If the allocation breaks the contig_hint, a scan is required to > > - * restore this hint. > > */ > > if (s_block->contig_hint == PCPU_BITMAP_BLOCK_BITS) > > nr_empty_pages++; > > > > + /* > > + * block->first_free must be updated if the allocation takes its place. > > + * If the allocation breaks the contig_hint, a scan is required to > > + * restore this hint. > > + */ > > if (s_off == s_block->first_free) > > s_block->first_free = find_next_zero_bit( > > pcpu_index_alloc_map(chunk, s_index), > > @@ -912,6 +914,12 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off, > > } > > } > > > > + /* > > + * If the allocation is not atomic, some blocks may not > > + * be populated with pages, while we account it here. > > + * The number of pages will be subtracted with > > + * pcpu_chunk_populated() when populating pages. > > + */ > > if (nr_empty_pages) > > pcpu_update_empty_pages(chunk, -nr_empty_pages); > > > > -- > > 2.34.1 > > > > Heh, that's a little more subtle than I remember it being. > > Acked-by: Dennis Zhou Thanks for reviewing, Dennis. When I rechecked the code comment, I realized I had said the opposite in v1 about the newly added code comment. It subtracts the nr_empty_pop_pages in pcpu_block_update_hint_alloc() whether it's atomic allocation or not. If non atomic case, the number will be added back in pcpu_chunk_populated() when populating pages. I have updated and resent v2, sorry for the mistake. Thanks Baoquan