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 5950EC43334 for ; Tue, 21 Jun 2022 11:32:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348722AbiFULcK (ORCPT ); Tue, 21 Jun 2022 07:32:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44610 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230429AbiFULcI (ORCPT ); Tue, 21 Jun 2022 07:32:08 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3029DB4BD for ; Tue, 21 Jun 2022 04:32:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1655811126; 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=Y1o/jnMsU4IPX6HlOfyZ4A2cxwPbVUo4lnU9g11rsaY=; b=AVky9HMFWva5LKXy4jWF5FrYA9uKcD45QmNzYbZV/SIOCFt62PzWnrr85Aigt28LvQxY5S VtTVrx4YLLNjA6LjdkbQb1JrtztcJ78Ujoo2WLv6Qug5SDNAPq4lH86uq4fGd6frmHHRnZ EVAC7H8HJrLImAWVYbSck1kb0IP6RzQ= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-631-4hH46OeWM0W6UtgB_TVpdw-1; Tue, 21 Jun 2022 07:32:05 -0400 X-MC-Unique: 4hH46OeWM0W6UtgB_TVpdw-1 Received: by mail-wm1-f72.google.com with SMTP id k16-20020a7bc310000000b0038e6cf00439so6286942wmj.0 for ; Tue, 21 Jun 2022 04:32:04 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:organization:in-reply-to :content-transfer-encoding; bh=Y1o/jnMsU4IPX6HlOfyZ4A2cxwPbVUo4lnU9g11rsaY=; b=PVrGmoV6AdMQtZcB43MCKJAKgfHA60lq7QXxSJ9JFzMLZNpTpzz0KdBg44N3+Xev0F hwk2qslaXXIgUbnQ+Jt6ACUi1CvygvD0bIQurHG47HVmnIwiF/7g+LxYRGzAvAgHkL+c rHf1ny2MFQJCx3DHUUVNkNaySH5d6hJ2UF3hWn3jyO/wccqTShohBEB/tC159HQo9NKW exNZq0JFx+w0nyCt7e4GV1oyp/b6a69Dv59/0+9EM/6qXPUiYAj3OLanuSFKhsbpv3wW KdK9rqbh/PN64nZTGMPyQL/L+kt4fA1BxlG2nnugqETaKERCVfIxtuLg5aeFwv66aOld pvLQ== X-Gm-Message-State: AJIora9/bh8jFRHGnHfZLw7JQyinwdSKygWH3aeUZ5YiMRqrK+83Ortl l0w4E29tYX+CAG0Z3rtJfuwyCzdjBQO6lu/tdMB036yjIeZU0N5zxdBnrDrwWTNsxsPrA8Rcxw9 nwYx+dgENYHF/mAvdu+HHzg== X-Received: by 2002:adf:fb0b:0:b0:21a:b15:6013 with SMTP id c11-20020adffb0b000000b0021a0b156013mr27217782wrr.268.1655811123765; Tue, 21 Jun 2022 04:32:03 -0700 (PDT) X-Google-Smtp-Source: AGRyM1vID2DBhF1VSe6FJYOzJsuR+237Ihfn2g9rXPagZ5JJL2QI2dXrP9uXmyixWi9QK60Zpdz4lA== X-Received: by 2002:adf:fb0b:0:b0:21a:b15:6013 with SMTP id c11-20020adffb0b000000b0021a0b156013mr27217746wrr.268.1655811123386; Tue, 21 Jun 2022 04:32:03 -0700 (PDT) Received: from ?IPV6:2003:d8:2f04:2500:cdb0:9b78:d423:43f? 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[2003:d8:2f04:2500:cdb0:9b78:d423:43f]) by smtp.gmail.com with ESMTPSA id o1-20020adfeac1000000b0021b8c554196sm7228854wrn.29.2022.06.21.04.32.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jun 2022 04:32:02 -0700 (PDT) Message-ID: <34e94bdb-675a-5d5c-6137-8aa1ee658d49@redhat.com> Date: Tue, 21 Jun 2022 13:32:02 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v5 01/13] mm: add zone device coherent type memory support Content-Language: en-US To: Felix Kuehling , "Sierra Guiza, Alejandro (Alex)" , jgg@nvidia.com Cc: linux-mm@kvack.org, rcampbell@nvidia.com, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, hch@lst.de, jglisse@redhat.com, apopple@nvidia.com, willy@infradead.org, akpm@linux-foundation.org References: <20220531200041.24904-1-alex.sierra@amd.com> <20220531200041.24904-2-alex.sierra@amd.com> <3ac89358-2ce0-7d0d-8b9c-8b0e5cc48945@redhat.com> <02ed2cb7-3ad3-8ffc-6032-04ae1853e234@amd.com> <7605beee-0a76-4ee9-e950-17419630f2cf@redhat.com> <6aef4b7f-0ced-08cd-1f0c-50c22996aa41@redhat.com> <65987ab8-426d-e533-0295-069312b4f751@amd.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <65987ab8-426d-e533-0295-069312b4f751@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On 21.06.22 13:25, Felix Kuehling wrote: > > Am 6/17/22 um 23:19 schrieb David Hildenbrand: >> On 17.06.22 21:27, Sierra Guiza, Alejandro (Alex) wrote: >>> On 6/17/2022 12:33 PM, David Hildenbrand wrote: >>>> On 17.06.22 19:20, Sierra Guiza, Alejandro (Alex) wrote: >>>>> On 6/17/2022 4:40 AM, David Hildenbrand wrote: >>>>>> On 31.05.22 22:00, Alex Sierra wrote: >>>>>>> Device memory that is cache coherent from device and CPU point of view. >>>>>>> This is used on platforms that have an advanced system bus (like CAPI >>>>>>> or CXL). Any page of a process can be migrated to such memory. However, >>>>>>> no one should be allowed to pin such memory so that it can always be >>>>>>> evicted. >>>>>>> >>>>>>> Signed-off-by: Alex Sierra >>>>>>> Acked-by: Felix Kuehling >>>>>>> Reviewed-by: Alistair Popple >>>>>>> [hch: rebased ontop of the refcount changes, >>>>>>> removed is_dev_private_or_coherent_page] >>>>>>> Signed-off-by: Christoph Hellwig >>>>>>> --- >>>>>>> include/linux/memremap.h | 19 +++++++++++++++++++ >>>>>>> mm/memcontrol.c | 7 ++++--- >>>>>>> mm/memory-failure.c | 8 ++++++-- >>>>>>> mm/memremap.c | 10 ++++++++++ >>>>>>> mm/migrate_device.c | 16 +++++++--------- >>>>>>> mm/rmap.c | 5 +++-- >>>>>>> 6 files changed, 49 insertions(+), 16 deletions(-) >>>>>>> >>>>>>> diff --git a/include/linux/memremap.h b/include/linux/memremap.h >>>>>>> index 8af304f6b504..9f752ebed613 100644 >>>>>>> --- a/include/linux/memremap.h >>>>>>> +++ b/include/linux/memremap.h >>>>>>> @@ -41,6 +41,13 @@ struct vmem_altmap { >>>>>>> * A more complete discussion of unaddressable memory may be found in >>>>>>> * include/linux/hmm.h and Documentation/vm/hmm.rst. >>>>>>> * >>>>>>> + * MEMORY_DEVICE_COHERENT: >>>>>>> + * Device memory that is cache coherent from device and CPU point of view. This >>>>>>> + * is used on platforms that have an advanced system bus (like CAPI or CXL). A >>>>>>> + * driver can hotplug the device memory using ZONE_DEVICE and with that memory >>>>>>> + * type. Any page of a process can be migrated to such memory. However no one >>>>>> Any page might not be right, I'm pretty sure. ... just thinking about special pages >>>>>> like vdso, shared zeropage, ... pinned pages ... >>>> Well, you cannot migrate long term pages, that's what I meant :) >>>> >>>>>>> + * should be allowed to pin such memory so that it can always be evicted. >>>>>>> + * >>>>>>> * MEMORY_DEVICE_FS_DAX: >>>>>>> * Host memory that has similar access semantics as System RAM i.e. DMA >>>>>>> * coherent and supports page pinning. In support of coordinating page >>>>>>> @@ -61,6 +68,7 @@ struct vmem_altmap { >>>>>>> enum memory_type { >>>>>>> /* 0 is reserved to catch uninitialized type fields */ >>>>>>> MEMORY_DEVICE_PRIVATE = 1, >>>>>>> + MEMORY_DEVICE_COHERENT, >>>>>>> MEMORY_DEVICE_FS_DAX, >>>>>>> MEMORY_DEVICE_GENERIC, >>>>>>> MEMORY_DEVICE_PCI_P2PDMA, >>>>>>> @@ -143,6 +151,17 @@ static inline bool folio_is_device_private(const struct folio *folio) >>>>>> In general, this LGTM, and it should be correct with PageAnonExclusive I think. >>>>>> >>>>>> >>>>>> However, where exactly is pinning forbidden? >>>>> Long-term pinning is forbidden since it would interfere with the device >>>>> memory manager owning the >>>>> device-coherent pages (e.g. evictions in TTM). However, normal pinning >>>>> is allowed on this device type. >>>> I don't see updates to folio_is_pinnable() in this patch. >>> Device coherent type pages should return true here, as they are pinnable >>> pages. >> That function is only called for long-term pinnings in try_grab_folio(). >> >>>> So wouldn't try_grab_folio() simply pin these pages? What am I missing? >>> As far as I understand this return NULL for long term pin pages. >>> Otherwise they get refcount incremented. >> I don't follow. >> >> You're saying >> >> a) folio_is_pinnable() returns true for device coherent pages >> >> and that >> >> b) device coherent pages don't get long-term pinned >> >> >> Yet, the code says >> >> struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags) >> { >> if (flags & FOLL_GET) >> return try_get_folio(page, refs); >> else if (flags & FOLL_PIN) { >> struct folio *folio; >> >> /* >> * Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a >> * right zone, so fail and let the caller fall back to the slow >> * path. >> */ >> if (unlikely((flags & FOLL_LONGTERM) && >> !is_pinnable_page(page))) >> return NULL; >> ... >> return folio; >> } >> } >> >> >> What prevents these pages from getting long-term pinned as stated in this patch? > > Long-term pinning is handled by __gup_longterm_locked, which migrates > pages returned by __get_user_pages_locked that cannot be long-term > pinned. try_grab_folio is OK to grab the pages. Anything that can't be > long-term pinned will be migrated afterwards, and > __get_user_pages_locked will be retried. The migration of > DEVICE_COHERENT pages was implemented by Alistair in patch 5/13 > ("mm/gup: migrate device coherent pages when pinning instead of failing"). Thanks. __gup_longterm_locked()->check_and_migrate_movable_pages() Which checks folio_is_pinnable() and doesn't do anything if set. Sorry to be dense here, but I don't see how what's stated in this patch works without adjusting folio_is_pinnable(). -- Thanks, David / dhildenb 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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 50105C43334 for ; Tue, 21 Jun 2022 11:32:09 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 85D2210F6E4; Tue, 21 Jun 2022 11:32:08 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id 1A70B10F6E4 for ; Tue, 21 Jun 2022 11:32:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1655811126; 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=Y1o/jnMsU4IPX6HlOfyZ4A2cxwPbVUo4lnU9g11rsaY=; b=AVky9HMFWva5LKXy4jWF5FrYA9uKcD45QmNzYbZV/SIOCFt62PzWnrr85Aigt28LvQxY5S VtTVrx4YLLNjA6LjdkbQb1JrtztcJ78Ujoo2WLv6Qug5SDNAPq4lH86uq4fGd6frmHHRnZ EVAC7H8HJrLImAWVYbSck1kb0IP6RzQ= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-631-6XwOpMg_MeOHSDZwnZdb5Q-1; Tue, 21 Jun 2022 07:32:05 -0400 X-MC-Unique: 6XwOpMg_MeOHSDZwnZdb5Q-1 Received: by mail-wr1-f71.google.com with SMTP id n5-20020adf8b05000000b00219ece7272bso3142875wra.8 for ; Tue, 21 Jun 2022 04:32:04 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:organization:in-reply-to :content-transfer-encoding; bh=Y1o/jnMsU4IPX6HlOfyZ4A2cxwPbVUo4lnU9g11rsaY=; b=tWj1/ZiozLKsTQM68EB8JzUdxfBeOvNdqFVFVYwwI8ozcphRI4kl8o2E0pqp3pOW64 pYdkrQfJDVxh0rDDXsN8O+GW5GnzehoR5wdvHufxRZI6f7tJrCM5SwLEaHBKOXT4RAwS B9em7BMiOPdXZ0QfE23TPE3ZMJLBNKL0VH6zPu1u01tcSyFIeAq76kklVbFhZ1UKRHW5 4XaR6M3/C0alpRoMgGbdmP3wSncrSvvbPFdAKbP5Druq76OYCIjsYsvJoTMXIMQPn7rv RTo5nNQDPqWzAib8VfxNDht9Wo+zM9Cy1APuAAzmGGpjg+HPR5vgJPJgk7CKYSnM492M ICfA== X-Gm-Message-State: AJIora9OdXJW203jQx5q8D5eeafKFpps3iD/M3iznFcFfIzKqOVaSeOA /AfwTYPkkh3R24EPsuj4jcM8DHJVS4+E1N4j93BNkPdNSx7D3rBWfUeepFsv35vWo76PlcB+TmG moxZjAJ+1UKPANfUBKUrjFJBsA6EX X-Received: by 2002:adf:fb0b:0:b0:21a:b15:6013 with SMTP id c11-20020adffb0b000000b0021a0b156013mr27217781wrr.268.1655811123765; Tue, 21 Jun 2022 04:32:03 -0700 (PDT) X-Google-Smtp-Source: AGRyM1vID2DBhF1VSe6FJYOzJsuR+237Ihfn2g9rXPagZ5JJL2QI2dXrP9uXmyixWi9QK60Zpdz4lA== X-Received: by 2002:adf:fb0b:0:b0:21a:b15:6013 with SMTP id c11-20020adffb0b000000b0021a0b156013mr27217746wrr.268.1655811123386; Tue, 21 Jun 2022 04:32:03 -0700 (PDT) Received: from ?IPV6:2003:d8:2f04:2500:cdb0:9b78:d423:43f? 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[2003:d8:2f04:2500:cdb0:9b78:d423:43f]) by smtp.gmail.com with ESMTPSA id o1-20020adfeac1000000b0021b8c554196sm7228854wrn.29.2022.06.21.04.32.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jun 2022 04:32:02 -0700 (PDT) Message-ID: <34e94bdb-675a-5d5c-6137-8aa1ee658d49@redhat.com> Date: Tue, 21 Jun 2022 13:32:02 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v5 01/13] mm: add zone device coherent type memory support To: Felix Kuehling , "Sierra Guiza, Alejandro (Alex)" , jgg@nvidia.com References: <20220531200041.24904-1-alex.sierra@amd.com> <20220531200041.24904-2-alex.sierra@amd.com> <3ac89358-2ce0-7d0d-8b9c-8b0e5cc48945@redhat.com> <02ed2cb7-3ad3-8ffc-6032-04ae1853e234@amd.com> <7605beee-0a76-4ee9-e950-17419630f2cf@redhat.com> <6aef4b7f-0ced-08cd-1f0c-50c22996aa41@redhat.com> <65987ab8-426d-e533-0295-069312b4f751@amd.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <65987ab8-426d-e533-0295-069312b4f751@amd.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: rcampbell@nvidia.com, willy@infradead.org, apopple@nvidia.com, dri-devel@lists.freedesktop.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org, jglisse@redhat.com, amd-gfx@lists.freedesktop.org, akpm@linux-foundation.org, linux-ext4@vger.kernel.org, hch@lst.de Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 21.06.22 13:25, Felix Kuehling wrote: > > Am 6/17/22 um 23:19 schrieb David Hildenbrand: >> On 17.06.22 21:27, Sierra Guiza, Alejandro (Alex) wrote: >>> On 6/17/2022 12:33 PM, David Hildenbrand wrote: >>>> On 17.06.22 19:20, Sierra Guiza, Alejandro (Alex) wrote: >>>>> On 6/17/2022 4:40 AM, David Hildenbrand wrote: >>>>>> On 31.05.22 22:00, Alex Sierra wrote: >>>>>>> Device memory that is cache coherent from device and CPU point of view. >>>>>>> This is used on platforms that have an advanced system bus (like CAPI >>>>>>> or CXL). Any page of a process can be migrated to such memory. However, >>>>>>> no one should be allowed to pin such memory so that it can always be >>>>>>> evicted. >>>>>>> >>>>>>> Signed-off-by: Alex Sierra >>>>>>> Acked-by: Felix Kuehling >>>>>>> Reviewed-by: Alistair Popple >>>>>>> [hch: rebased ontop of the refcount changes, >>>>>>> removed is_dev_private_or_coherent_page] >>>>>>> Signed-off-by: Christoph Hellwig >>>>>>> --- >>>>>>> include/linux/memremap.h | 19 +++++++++++++++++++ >>>>>>> mm/memcontrol.c | 7 ++++--- >>>>>>> mm/memory-failure.c | 8 ++++++-- >>>>>>> mm/memremap.c | 10 ++++++++++ >>>>>>> mm/migrate_device.c | 16 +++++++--------- >>>>>>> mm/rmap.c | 5 +++-- >>>>>>> 6 files changed, 49 insertions(+), 16 deletions(-) >>>>>>> >>>>>>> diff --git a/include/linux/memremap.h b/include/linux/memremap.h >>>>>>> index 8af304f6b504..9f752ebed613 100644 >>>>>>> --- a/include/linux/memremap.h >>>>>>> +++ b/include/linux/memremap.h >>>>>>> @@ -41,6 +41,13 @@ struct vmem_altmap { >>>>>>> * A more complete discussion of unaddressable memory may be found in >>>>>>> * include/linux/hmm.h and Documentation/vm/hmm.rst. >>>>>>> * >>>>>>> + * MEMORY_DEVICE_COHERENT: >>>>>>> + * Device memory that is cache coherent from device and CPU point of view. This >>>>>>> + * is used on platforms that have an advanced system bus (like CAPI or CXL). A >>>>>>> + * driver can hotplug the device memory using ZONE_DEVICE and with that memory >>>>>>> + * type. Any page of a process can be migrated to such memory. However no one >>>>>> Any page might not be right, I'm pretty sure. ... just thinking about special pages >>>>>> like vdso, shared zeropage, ... pinned pages ... >>>> Well, you cannot migrate long term pages, that's what I meant :) >>>> >>>>>>> + * should be allowed to pin such memory so that it can always be evicted. >>>>>>> + * >>>>>>> * MEMORY_DEVICE_FS_DAX: >>>>>>> * Host memory that has similar access semantics as System RAM i.e. DMA >>>>>>> * coherent and supports page pinning. In support of coordinating page >>>>>>> @@ -61,6 +68,7 @@ struct vmem_altmap { >>>>>>> enum memory_type { >>>>>>> /* 0 is reserved to catch uninitialized type fields */ >>>>>>> MEMORY_DEVICE_PRIVATE = 1, >>>>>>> + MEMORY_DEVICE_COHERENT, >>>>>>> MEMORY_DEVICE_FS_DAX, >>>>>>> MEMORY_DEVICE_GENERIC, >>>>>>> MEMORY_DEVICE_PCI_P2PDMA, >>>>>>> @@ -143,6 +151,17 @@ static inline bool folio_is_device_private(const struct folio *folio) >>>>>> In general, this LGTM, and it should be correct with PageAnonExclusive I think. >>>>>> >>>>>> >>>>>> However, where exactly is pinning forbidden? >>>>> Long-term pinning is forbidden since it would interfere with the device >>>>> memory manager owning the >>>>> device-coherent pages (e.g. evictions in TTM). However, normal pinning >>>>> is allowed on this device type. >>>> I don't see updates to folio_is_pinnable() in this patch. >>> Device coherent type pages should return true here, as they are pinnable >>> pages. >> That function is only called for long-term pinnings in try_grab_folio(). >> >>>> So wouldn't try_grab_folio() simply pin these pages? What am I missing? >>> As far as I understand this return NULL for long term pin pages. >>> Otherwise they get refcount incremented. >> I don't follow. >> >> You're saying >> >> a) folio_is_pinnable() returns true for device coherent pages >> >> and that >> >> b) device coherent pages don't get long-term pinned >> >> >> Yet, the code says >> >> struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags) >> { >> if (flags & FOLL_GET) >> return try_get_folio(page, refs); >> else if (flags & FOLL_PIN) { >> struct folio *folio; >> >> /* >> * Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a >> * right zone, so fail and let the caller fall back to the slow >> * path. >> */ >> if (unlikely((flags & FOLL_LONGTERM) && >> !is_pinnable_page(page))) >> return NULL; >> ... >> return folio; >> } >> } >> >> >> What prevents these pages from getting long-term pinned as stated in this patch? > > Long-term pinning is handled by __gup_longterm_locked, which migrates > pages returned by __get_user_pages_locked that cannot be long-term > pinned. try_grab_folio is OK to grab the pages. Anything that can't be > long-term pinned will be migrated afterwards, and > __get_user_pages_locked will be retried. The migration of > DEVICE_COHERENT pages was implemented by Alistair in patch 5/13 > ("mm/gup: migrate device coherent pages when pinning instead of failing"). Thanks. __gup_longterm_locked()->check_and_migrate_movable_pages() Which checks folio_is_pinnable() and doesn't do anything if set. Sorry to be dense here, but I don't see how what's stated in this patch works without adjusting folio_is_pinnable(). -- Thanks, David / dhildenb