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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 00CB4C83F12 for ; Mon, 28 Aug 2023 11:48:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231266AbjH1Lr4 (ORCPT ); Mon, 28 Aug 2023 07:47:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48136 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232634AbjH1Lro (ORCPT ); Mon, 28 Aug 2023 07:47:44 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A2F9BCE8 for ; Mon, 28 Aug 2023 04:47:21 -0700 (PDT) Received: from localhost (unknown [IPv6:2a01:e0a:2c:6930:5cf4:84a1:2763:fe0d]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by madras.collabora.co.uk (Postfix) with ESMTPSA id EC92F660719F; Mon, 28 Aug 2023 12:46:56 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1693223217; bh=t2fCeu+OfukEEpqeGoqYnE46rRWxUmeM0L2SCqoD4uQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=AVRJUVWZMWdkkNkIwwQjHv2g46uUBb/77nyHYnON5KmS3tg1oGugPtkkG4iy1uFnG kTlb7OcbTpp1xrWuUx1KJtpRSrF1SGbMkVsAeizaiKACfM9cB68eq5B66FxW/z0+7+ rahTU6MwaXdpYMvnA/jTzBi28EoNNGrm4GKtg7sBMn6mw2AUMannZ0SwQa2OdVBM8v FDYapcT8+ESaQfWnpqZaOOsfWDIrV80adNPo2nlmyNaIV7hhiCZq6dzw4BFYNW34Vp tnh+hpKP8Z/thw5o3hGvTMbyi34lpKi1lsc4s0MRM+WhRqdPxxGwXrcw3Kt75gWZGY ss6gwo1Ls2YNw== Date: Mon, 28 Aug 2023 13:46:54 +0200 From: Boris Brezillon To: Dmitry Osipenko Cc: David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Christian =?UTF-8?B?S8O2bmln?= , Qiang Yu , Steven Price , Emma Anholt , Melissa Wen , Will Deacon , Peter Zijlstra , Boqun Feng , Mark Rutland , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org, intel-gfx@lists.freedesktop.org Subject: Re: [PATCH v15 12/23] drm/shmem-helper: Add and use pages_pin_count Message-ID: <20230828134654.7a2c6414@collabora.com> In-Reply-To: <20230827175449.1766701-13-dmitry.osipenko@collabora.com> References: <20230827175449.1766701-1-dmitry.osipenko@collabora.com> <20230827175449.1766701-13-dmitry.osipenko@collabora.com> Organization: Collabora X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 27 Aug 2023 20:54:38 +0300 Dmitry Osipenko wrote: > Add separate pages_pin_count for tracking of whether drm-shmem pages are > moveable or not. With the addition of memory shrinker support to drm-shmem, > the pages_use_count will no longer determine whether pages are hard-pinned > in memory, but whether pages exit and are soft-pinned (and could be swapped > out). The pages_pin_count > 1 will hard-pin pages in memory. > > Suggested-by: Boris Brezillon > Signed-off-by: Dmitry Osipenko > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 22 +++++++++++++++++----- > include/drm/drm_gem_shmem_helper.h | 10 ++++++++++ > 2 files changed, 27 insertions(+), 5 deletions(-) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index d545d3d227d7..1a7e5c332fd8 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -234,14 +234,22 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem) > > dma_resv_assert_held(shmem->base.resv); > > + if (kref_get_unless_zero(&shmem->pages_pin_count)) > + return 0; > + > ret = drm_gem_shmem_get_pages_locked(shmem); > + if (!ret) > + kref_init(&shmem->pages_pin_count); > > return ret; > } > > -static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem) > +static void drm_gem_shmem_kref_unpin_pages(struct kref *kref) > { > - dma_resv_assert_held(shmem->base.resv); > + struct drm_gem_shmem_object *shmem; > + > + shmem = container_of(kref, struct drm_gem_shmem_object, > + pages_pin_count); > > drm_gem_shmem_put_pages_locked(shmem); > } > @@ -263,6 +271,9 @@ int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem) > > drm_WARN_ON(obj->dev, obj->import_attach); > > + if (kref_get_unless_zero(&shmem->pages_pin_count)) > + return 0; > + > ret = dma_resv_lock_interruptible(shmem->base.resv, NULL); > if (ret) > return ret; > @@ -286,9 +297,10 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem) > > drm_WARN_ON(obj->dev, obj->import_attach); > > - dma_resv_lock(shmem->base.resv, NULL); > - drm_gem_shmem_unpin_locked(shmem); > - dma_resv_unlock(shmem->base.resv); > + if (kref_put_dma_resv(&shmem->pages_pin_count, > + drm_gem_shmem_kref_unpin_pages, > + obj->resv, NULL)) > + dma_resv_unlock(obj->resv); > } > EXPORT_SYMBOL_GPL(drm_gem_shmem_unpin); > > diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h > index ec2d8b24e3cf..afb7cd671e2a 100644 > --- a/include/drm/drm_gem_shmem_helper.h > +++ b/include/drm/drm_gem_shmem_helper.h > @@ -39,6 +39,16 @@ struct drm_gem_shmem_object { > */ > unsigned int pages_use_count; > > + /** > + * @pages_pin_count: > + * > + * Reference count on the pinned pages table. > + * The pages allowed to be evicted and purged by memory > + * shrinker only when the count is zero, otherwise pages > + * are hard-pinned in memory. > + */ > + struct kref pages_pin_count; I know it's tempting to use kref for the pages use/pin count, but I'm wondering if we wouldn't be better using a refcount_t, which provides overflow/underflow protection while still letting us control how we want to handle the locking for 0 <-> 1 transitions. By doing that, we avoid introducing core locking changes that might be more controversial/longer to get accepted. Besides, I suspect the resulting code (the one using a refcount_t) won't be more verbose/complicated (no release functions needed if you don't use kref_put(), which makes things closer to what we have right now). > + > /** > * @madv: State for madvise > *