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=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 61ECFC433DB for ; Mon, 22 Feb 2021 11:44:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1AFA664E77 for ; Mon, 22 Feb 2021 11:44:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230045AbhBVLok (ORCPT ); Mon, 22 Feb 2021 06:44:40 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:40075 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229918AbhBVLoi (ORCPT ); Mon, 22 Feb 2021 06:44:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613994192; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=MmzZCjQQYbObSyV51XAvsCh6DM7Wnhv+Pu08wvezplw=; b=hSSb8Nm6yeDTVyHjQGbr+ODepJ0TwSkaAz3nuzN7ffmdmInsAVzO5hR+dlGwcBAbBca9VH ZiXATQLWCibddCTEnUmi5TLl6sqIAYe0syYam51CJ0NZW3QiXzzfdOpmLe8+/7z8jJ7+Hq 7JG1o88Viz9AgT/n1/iMKBfiPcNbH20= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-486-41D8J8JmPjKTNYMKtidFaQ-1; Mon, 22 Feb 2021 06:43:09 -0500 X-MC-Unique: 41D8J8JmPjKTNYMKtidFaQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 45731102C7F4; Mon, 22 Feb 2021 11:43:07 +0000 (UTC) Received: from carbon (unknown [10.36.110.50]) by smtp.corp.redhat.com (Postfix) with ESMTP id 04C861F0; Mon, 22 Feb 2021 11:42:57 +0000 (UTC) Date: Mon, 22 Feb 2021 12:42:46 +0100 From: Jesper Dangaard Brouer To: Mel Gorman Cc: Chuck Lever , Mel Gorman , Linux NFS Mailing List , "linux-mm@kvack.org" , Jakub Kicinski , brouer@redhat.com, "netdev@vger.kernel.org" Subject: Re: alloc_pages_bulk() Message-ID: <20210222124246.690414a2@carbon> In-Reply-To: <20210222094256.GH3697@techsingularity.net> References: <20210209113108.1ca16cfa@carbon> <20210210084155.GA3697@techsingularity.net> <20210210124103.56ed1e95@carbon> <20210210130705.GC3629@suse.de> <20210211091235.GC3697@techsingularity.net> <20210211132628.1fe4f10b@carbon> <20210215120056.GD3697@techsingularity.net> <20210215171038.42f62438@carbon> <20210222094256.GH3697@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Mon, 22 Feb 2021 09:42:56 +0000 Mel Gorman wrote: > On Mon, Feb 15, 2021 at 05:10:38PM +0100, Jesper Dangaard Brouer wrote: > > > > On Mon, 15 Feb 2021 12:00:56 +0000 > > Mel Gorman wrote: > > > > > On Thu, Feb 11, 2021 at 01:26:28PM +0100, Jesper Dangaard Brouer wrote: > > [...] > > > > > > > I also suggest the API can return less pages than requested. Because I > > > > want to to "exit"/return if it need to go into an expensive code path > > > > (like buddy allocator or compaction). I'm assuming we have a flags to > > > > give us this behavior (via gfp_flags or alloc_flags)? > > > > > > > > > > The API returns the number of pages returned on a list so policies > > > around how aggressive it should be allocating the requested number of > > > pages could be adjusted without changing the API. Passing in policy > > > requests via gfp_flags may be problematic as most (all?) bits are > > > already used. > > > > Well, I was just thinking that I would use GFP_ATOMIC instead of > > GFP_KERNEL to "communicate" that I don't want this call to take too > > long (like sleeping). I'm not requesting any fancy policy :-) > > > > The NFS use case requires opposite semantics > -- it really needs those allocations to succeed > https://lore.kernel.org/r/161340498400.7780.962495219428962117.stgit@klimt.1015granger.net. Sorry, but that is not how I understand the code. The code is doing exactly what I'm requesting. If the alloc_pages_bulk() doesn't return expected number of pages, then check if others need to run. The old code did schedule_timeout(msecs_to_jiffies(500)), while Chuck's patch change this to ask for cond_resched(). Thus, it tries to avoid blocking the CPU for too long (when allocating many pages). And the nfsd code seems to handle that the code can be interrupted (via return -EINTR) via signal_pending(current). Thus, the nfsd code seems to be able to handle if the page allocations failed. > I've asked what code it's based on as it's not 5.11 and I'll iron that > out first. > > Then it might be clearer what the "can fail" semantics should look like. > I think it would be best to have pairs of patches where the first patch > adjusts the semantics of the bulk allocator and the second adds a user. > That will limit the amount of code code carried in the implementation. > When the initial users are in place then the implementation can be > optimised as the optimisations will require significant refactoring and > I not want to refactor multiple times. I guess, I should try to code-up the usage in page_pool. What is the latest patch for adding alloc_pages_bulk() ? The nfsd code (svc_alloc_arg) is called in a context where it can sleep, and thus use GFP_KERNEL. In most cases the page_pool will be called with GFP_ATOMIC. I don't think I/page_pool will retry the call like Chuck did, as I cannot (re)schedule others to run. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer