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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 4FAC2C433E0 for ; Thu, 2 Jul 2020 21:55:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 224AB214DB for ; Thu, 2 Jul 2020 21:55:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593726906; bh=3Eexubn3sZVVapBb4ocw+zEhYZY1y/b44i54tLIxOro=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=qGWtWqucWQci9zBLs4SgXmQmE5vzc29xsWOAfhW+SEDLLOzSmpEPiKGpCHi7AKEeO Tae7gvRAH8cJJlf5lUI66MWsEwwsRG50zJslpZfKX1tOyWfVshiGc5G9GIeanAM04T tJqGoqUGw2N2xfRwuFFW3mgURIq5YWfIpaqnkUCI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726003AbgGBVzF (ORCPT ); Thu, 2 Jul 2020 17:55:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:52212 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725937AbgGBVzF (ORCPT ); Thu, 2 Jul 2020 17:55:05 -0400 Received: from kernel.org (unknown [87.71.40.38]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1CCC820B1F; Thu, 2 Jul 2020 21:55:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593726904; bh=3Eexubn3sZVVapBb4ocw+zEhYZY1y/b44i54tLIxOro=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=B8KFhdGelPo+xUUHYoaaZmAuYt7bMlVD/m5FcGTZ8BrcQ1AVkN6rEIEQqskmJd/Tq BXc82HKVB70T418+iMPes3f23vXNiT3roZAXRLJbvc1RzuYCeNTQJjTPxa1Y6al/Ob ZYgP5vpOh2QO2wXA8N+NiHpXZrqOpnAIeGK5JEtM= Date: Fri, 3 Jul 2020 00:54:59 +0300 From: Mike Rapoport To: Jonathan Corbet Cc: Michal Hocko , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Mike Rapoport Subject: Re: [PATCH] docs/core-api: memory-allocation: describe reclaim behaviour Message-ID: <20200702215459.GD2999148@kernel.org> References: <20200626142950.135184-1-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200626142950.135184-1-rppt@kernel.org> Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Gentle ping. On Fri, Jun 26, 2020 at 05:29:50PM +0300, Mike Rapoport wrote: > From: Mike Rapoport > > Changelog of commit dcda9b04713c ("mm, tree wide: replace __GFP_REPEAT by > __GFP_RETRY_MAYFAIL with more useful semantic") has very nice description > of GFP flags that affect reclaim behaviour of the page allocator. > > It would be pity to keep this description buried in the log so let's expose > it in the Documentation/ as well. > > Cc: Michal Hocko > Signed-off-by: Mike Rapoport > --- > Hi, > > I've been looking for something completely unrealated and found this > really nice piece of documentation. > > Thanks Michal! ;-) > > Documentation/core-api/memory-allocation.rst | 44 ++++++++++++++++++++ > 1 file changed, 44 insertions(+) > > diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst > index 4aa82ddd01b8..4446a1ac36cc 100644 > --- a/Documentation/core-api/memory-allocation.rst > +++ b/Documentation/core-api/memory-allocation.rst > @@ -84,6 +84,50 @@ driver for a device with such restrictions, avoid using these flags. > And even with hardware with restrictions it is preferable to use > `dma_alloc*` APIs. > > +GFP flags and reclaim behavior > +------------------------------ > +Memory allocations may trigger direct or background reclaim and it is > +useful to understand how hard the page allocator will try to satisfy that > +or another request. > + > + * ``GFP_KERNEL & ~__GFP_RECLAIM`` - optimistic allocation without _any_ > + attempt to free memory at all. The most light weight mode which even > + doesn't kick the background reclaim. Should be used carefully because it > + might deplete the memory and the next user might hit the more aggressive > + reclaim. > + > + * ``GFP_KERNEL & ~__GFP_DIRECT_RECLAIM`` (or ``GFP_NOWAIT``)- optimistic > + allocation without any attempt to free memory from the current > + context but can wake kswapd to reclaim memory if the zone is below > + the low watermark. Can be used from either atomic contexts or when > + the request is a performance optimization and there is another > + fallback for a slow path. > + > + * ``(GFP_KERNEL|__GFP_HIGH) & ~__GFP_DIRECT_RECLAIM`` (aka ``GFP_ATOMIC``) - > + non sleeping allocation with an expensive fallback so it can access > + some portion of memory reserves. Usually used from interrupt/bottom-half > + context with an expensive slow path fallback. > + > + * ``GFP_KERNEL`` - both background and direct reclaim are allowed and the > + **default** page allocator behavior is used. That means that not costly > + allocation requests are basically no-fail but there is no guarantee of > + that behavior so failures have to be checked properly by callers > + (e.g. OOM killer victim is allowed to fail currently). > + > + * ``GFP_KERNEL | __GFP_NORETRY`` - overrides the default allocator behavior > + and all allocation requests fail early rather than cause disruptive > + reclaim (one round of reclaim in this implementation). The OOM killer > + is not invoked. > + > + * ``GFP_KERNEL | __GFP_RETRY_MAYFAIL`` - overrides the default allocator > + behavior and all allocation requests try really hard. The request > + will fail if the reclaim cannot make any progress. The OOM killer > + won't be triggered. > + > + * ``GFP_KERNEL | __GFP_NOFAIL`` - overrides the default allocator behavior > + and all allocation requests will loop endlessly until they succeed. > + This might be really dangerous especially for larger orders. > + > Selecting memory allocator > ========================== > > -- > 2.25.4 > -- Sincerely yours, Mike.