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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 09662C433DF for ; Thu, 25 Jun 2020 13:11:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE81520702 for ; Thu, 25 Jun 2020 13:11:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="kzbXYUu5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404890AbgFYNLN (ORCPT ); Thu, 25 Jun 2020 09:11:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34522 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404783AbgFYNLN (ORCPT ); Thu, 25 Jun 2020 09:11:13 -0400 Received: from casper.infradead.org (unknown [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F3CDCC08C5C1; Thu, 25 Jun 2020 06:11:12 -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=lf76WPH88lH813mY9Yo8ZHZHFHxan9PWrz3Tg7MET60=; b=kzbXYUu53U2ernxrU8NemdCmxZ w8ncV08dVPq7jkm2cnmqpBU10R9U4MKgzsV3vbpTA/25y2MNDYhjdSx1ozsXt6oevq61pyUP0LFlN X1BMrmzYQVNWdH60xTMWVqG82GP+i/OC1pkmtsfLT7aQe54L7UFUGSlvQBNfREuI40WcjJPuruX2U FTQUv6+jqMK/G0pYgB6Nl2mc7FM/HNyXAcHxnU7/kNqND9/NyZMdZHvBn6HhSWlbaOJ/mVVcQu4FW 0S+3ys8xvGXnZwngL2GvKy4lY/uO6CH03hVI6iEklM4HtYBx89uulHC/8zCzBs9QJcScc77VI+vS0 rBYHy2Bw==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1joReZ-00077i-S6; Thu, 25 Jun 2020 13:10:55 +0000 Date: Thu, 25 Jun 2020 14:10:55 +0100 From: Matthew Wilcox To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-xfs@vger.kernel.org, dm-devel@redhat.com, Mikulas Patocka , Jens Axboe , NeilBrown Subject: Re: [PATCH 6/6] mm: Add memalloc_nowait Message-ID: <20200625131055.GC7703@casper.infradead.org> References: <20200625113122.7540-1-willy@infradead.org> <20200625113122.7540-7-willy@infradead.org> <20200625124017.GL1320@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200625124017.GL1320@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 25, 2020 at 02:40:17PM +0200, Michal Hocko wrote: > On Thu 25-06-20 12:31:22, Matthew Wilcox wrote: > > Similar to memalloc_noio() and memalloc_nofs(), memalloc_nowait() > > guarantees we will not sleep to reclaim memory. Use it to simplify > > dm-bufio's allocations. > > memalloc_nowait is a good idea! I suspect the primary usecase would be > vmalloc. That's funny. My use case is allocating page tables in an RCU protected page fault handler. Jens' use case is allocating page cache. This one is a vmalloc consumer (which is also indirectly page table allocation). > > @@ -877,7 +857,9 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client > > */ > > while (1) { > > if (dm_bufio_cache_size_latch != 1) { > > - b = alloc_buffer(c, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN); > > + unsigned nowait_flag = memalloc_nowait_save(); > > + b = alloc_buffer(c, GFP_KERNEL | __GFP_NOMEMALLOC | __GFP_NOWARN); > > + memalloc_nowait_restore(nowait_flag); > > This looks confusing though. I am not familiar with alloc_buffer and > there is quite some tweaking around __GFP_NORETRY in alloc_buffer_data > which I do not follow but GFP_KERNEL just struck my eyes. So why cannot > we have > alloc_buffer(GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_NOWARN); Actually, I wanted to ask about the proliferation of __GFP_NOMEMALLOC in the block layer. Am I right in thinking it really has no effect unless GFP_ATOMIC is set? It seems like a magic flag that some driver developers are sprinkling around randomly, so we probably need to clarify the documentation on it. What I was trying to do was just use the memalloc_nofoo API to control what was going on and then the driver can just use GFP_KERNEL. I should probably have completed that thought before sending the patches out.