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=-1.0 required=3.0 tests=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 DAF8DC433E0 for ; Wed, 24 Jun 2020 14:17:52 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BB7EC20781 for ; Wed, 24 Jun 2020 14:17:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BB7EC20781 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=chris-wilson.co.uk Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 65CC56B0006; Wed, 24 Jun 2020 10:17:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 60D196B0007; Wed, 24 Jun 2020 10:17:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 521766B0008; Wed, 24 Jun 2020 10:17:51 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0137.hostedemail.com [216.40.44.137]) by kanga.kvack.org (Postfix) with ESMTP id 38F446B0006 for ; Wed, 24 Jun 2020 10:17:51 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id D1F981C9A2 for ; Wed, 24 Jun 2020 14:17:50 +0000 (UTC) X-FDA: 76964309100.25.seed46_051214526e44 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin25.hostedemail.com (Postfix) with ESMTP id E0F311803A63F for ; Wed, 24 Jun 2020 14:12:54 +0000 (UTC) X-HE-Tag: seed46_051214526e44 X-Filterd-Recvd-Size: 2823 Received: from fireflyinternet.com (mail.fireflyinternet.com [109.228.58.192]) by imf09.hostedemail.com (Postfix) with ESMTP for ; Wed, 24 Jun 2020 14:12:54 +0000 (UTC) X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.65.138; Received: from localhost (unverified [78.156.65.138]) by fireflyinternet.com (Firefly Internet (M1)) with ESMTP (TLS) id 21603647-1500050 for multiple; Wed, 24 Jun 2020 15:12:46 +0100 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable In-Reply-To: <20200624123910.GA3178169@ziepe.ca> References: <20200624080248.3701-1-chris@chris-wilson.co.uk> <20200624121053.GD6578@ziepe.ca> <159300126338.4527.3968787379471939056@build.alporthouse.com> <20200624123910.GA3178169@ziepe.ca> From: Chris Wilson Subject: Re: [PATCH 1/2] mm/mmu_notifier: Mark up direct reclaim paths with MAYFAIL To: Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org, Andrew Morton Message-ID: <159300796224.4527.2014771396582759689@build.alporthouse.com> User-Agent: alot/0.8.1 Date: Wed, 24 Jun 2020 15:12:42 +0100 X-Rspamd-Queue-Id: E0F311803A63F X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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: Quoting Jason Gunthorpe (2020-06-24 13:39:10) > On Wed, Jun 24, 2020 at 01:21:03PM +0100, Chris Wilson wrote: > > Quoting Jason Gunthorpe (2020-06-24 13:10:53) > > > On Wed, Jun 24, 2020 at 09:02:47AM +0100, Chris Wilson wrote: > > > > When direct reclaim enters the shrinker and tries to reclaim pages,= it > > > > has to opportunitically unmap them [try_to_unmap_one]. For direct > > > > reclaim, the calling context is unknown and may include attempts to > > > > unmap one page of a dma object while attempting to allocate more pa= ges > > > > for that object. Pass the information along that we are inside an > > > > opportunistic unmap that can allow that page to remain referenced a= nd > > > > mapped, and let the callback opt in to avoiding a recursive wait. > > >=20 > > > i915 should already not be holding locks shared with the notifiers > > > across allocations that can trigger reclaim. This is already required > > > to use notifiers correctly anyhow - why do we need something in the > > > notifiers? > >=20 > > for (n =3D 0; n < num_pages; n++) > > pin_user_page() > >=20 > > may call try_to_unmap_page from the lru shrinker for [0, n-1]. >=20 > Yes, of course you can't hold any locks that intersect with notifiers > across pin_user_page()/get_user_page() What lock though? It's just the page refcount, shrinker asks us to drop it [via mmu], we reply we would like to keep using that page as freeing it for the current allocation is "robbing Peter to pay Paul". -Chris