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 A9B96C433DF for ; Thu, 25 Jun 2020 13:11:02 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5166D20702 for ; Thu, 25 Jun 2020 13:11:02 +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" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5166D20702 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9B3556B0082; Thu, 25 Jun 2020 09:11:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 93C446B0083; Thu, 25 Jun 2020 09:11:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 804C56B0085; Thu, 25 Jun 2020 09:11:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0203.hostedemail.com [216.40.44.203]) by kanga.kvack.org (Postfix) with ESMTP id 65F786B0082 for ; Thu, 25 Jun 2020 09:11:01 -0400 (EDT) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 16238180AC47E for ; Thu, 25 Jun 2020 13:11:01 +0000 (UTC) X-FDA: 76967769522.04.eyes24_0f09c4f26e4d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin04.hostedemail.com (Postfix) with ESMTP id DBD18801DC0B for ; Thu, 25 Jun 2020 13:11:00 +0000 (UTC) X-HE-Tag: eyes24_0f09c4f26e4d X-Filterd-Recvd-Size: 3630 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf41.hostedemail.com (Postfix) with ESMTP for ; Thu, 25 Jun 2020 13:11:00 +0000 (UTC) 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> X-Rspamd-Queue-Id: DBD18801DC0B X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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.