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 1225DC43334 for ; Tue, 21 Jun 2022 12:25:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350046AbiFUMZe (ORCPT ); Tue, 21 Jun 2022 08:25:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58212 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350008AbiFUMZc (ORCPT ); Tue, 21 Jun 2022 08:25:32 -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 97D94255B0 for ; Tue, 21 Jun 2022 05:25:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1655814329; 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=65Njp+ThqlVdqFDxuhaHtcra47G9ZdLFWICrTgPdMDI=; b=LrlmT0ZB9R28yuefufvjJ83xcGvWhVaWZF+KEyvGroKVkLAQPSo3tGSEFkFVK5VDWwUE9Q XZeAE89iPcVHiiJK6oiMzDa2ScVqrwfiDsKicZWicshfaapk4+gbazbM+FwJUnCAj9rAs6 XhljaHzZK1HA5VKKu47UbyukLLle+PE= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-315-eXPC7fnUM9SX1r5gg7dwpQ-1; Tue, 21 Jun 2022 08:25:28 -0400 X-MC-Unique: eXPC7fnUM9SX1r5gg7dwpQ-1 Received: by mail-wr1-f70.google.com with SMTP id w8-20020adfde88000000b00213b7fa3a37so3181306wrl.2 for ; Tue, 21 Jun 2022 05:25:28 -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=65Njp+ThqlVdqFDxuhaHtcra47G9ZdLFWICrTgPdMDI=; b=78Rd6T+z0EDe8mBipXZXhp69x3snDlY7uqw/DeuGCYawaztm2T8eK/3TAvhEaArB9O eoRY22vBM5/Sj4WRPUd3en8KNRDNg+/cirNYWJQ7GsPjEisk65hlaZTb+wRG+ugtzmK4 uKvBnxBKI2PFdjyFXRfC066Pv1ljYRj3DcXTzL31iSoxttOpFXCwogJbpRq4/y97PecM onfbZnJKJ9s00jLrb8FxEWKMb73wVlEIKorFhZWlWvYk2Ajx2z48KjxWHtZuA4KkipXj li7hONMzVTY4YS/eTvQbaDlRSBLWzTljfNm2ekfKoqqocXwt8v3849Qt6iCeE79ynkr3 27EQ== X-Gm-Message-State: AJIora8JvcCDSOnwcNWn+D0PV1rdnt39l0rDGG4NPSB/9VZtPVEKYJWr ozjsH7d/emP50KxijQVaO8IGRNIj4kosHLqz5aG2XuFiE57dXyuEbUu+wI0wssHVTsKSY8AqzNu XGjtwBythQQyK3WL4MBIpCg== X-Received: by 2002:adf:ffcf:0:b0:21a:3cc0:d624 with SMTP id x15-20020adfffcf000000b0021a3cc0d624mr23496568wrs.164.1655814327319; Tue, 21 Jun 2022 05:25:27 -0700 (PDT) X-Google-Smtp-Source: AGRyM1vHTlAgCbYSPwKOnD4wThbGsJJ+9XZS//2sA4ocZl1PpUmbJFPrznizqZ5xjm3YK7dzwI4CFQ== X-Received: by 2002:adf:ffcf:0:b0:21a:3cc0:d624 with SMTP id x15-20020adfffcf000000b0021a3cc0d624mr23496546wrs.164.1655814327013; Tue, 21 Jun 2022 05:25:27 -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 b5-20020a05600c4e0500b0039aef592ca0sm18064551wmq.35.2022.06.21.05.25.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jun 2022 05:25:26 -0700 (PDT) Message-ID: <643c44e7-48be-375b-c7ab-6a30b5ee2937@redhat.com> Date: Tue, 21 Jun 2022 14:25:25 +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: Alistair Popple Cc: Felix Kuehling , "Sierra Guiza, Alejandro (Alex)" , jgg@nvidia.com, 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, 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> <34e94bdb-675a-5d5c-6137-8aa1ee658d49@redhat.com> <87letq6wb5.fsf@nvdebian.thelocal> From: David Hildenbrand Organization: Red Hat In-Reply-To: <87letq6wb5.fsf@nvdebian.thelocal> 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 13:55, Alistair Popple wrote: > > David Hildenbrand writes: > >> 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(). > > Ugh, I think you might be right about try_grab_folio(). > > We didn't update folio_is_pinnable() to include device coherent pages > because device coherent pages are pinnable. It is really just > FOLL_LONGTERM that we want to prevent here. > > For normal PUP that is done by my change in > check_and_migrate_movable_pages() which migrates pages being pinned with > FOLL_LONGTERM. But I think I incorrectly assumed we would take the > pte_devmap() path in gup_pte_range(), which we don't for coherent pages. > So I think the check in try_grab_folio() needs to be: I think I said it already (and I might be wrong without reading the code), but folio_is_pinnable() is *only* called for long-term pinnings. It should actually be called folio_is_longterm_pinnable(). That's where that check should go, no? -- 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 AE3BAC43334 for ; Tue, 21 Jun 2022 12:25:32 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id BC8FA10F641; Tue, 21 Jun 2022 12:25:31 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id A65CA10F641 for ; Tue, 21 Jun 2022 12:25:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1655814329; 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=65Njp+ThqlVdqFDxuhaHtcra47G9ZdLFWICrTgPdMDI=; b=LrlmT0ZB9R28yuefufvjJ83xcGvWhVaWZF+KEyvGroKVkLAQPSo3tGSEFkFVK5VDWwUE9Q XZeAE89iPcVHiiJK6oiMzDa2ScVqrwfiDsKicZWicshfaapk4+gbazbM+FwJUnCAj9rAs6 XhljaHzZK1HA5VKKu47UbyukLLle+PE= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-208-SDdfhVbANmiW1-kmzyE9dw-1; Tue, 21 Jun 2022 08:25:28 -0400 X-MC-Unique: SDdfhVbANmiW1-kmzyE9dw-1 Received: by mail-wr1-f69.google.com with SMTP id i16-20020adfa510000000b0021b8e9f7666so1556805wrb.19 for ; Tue, 21 Jun 2022 05:25:28 -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=65Njp+ThqlVdqFDxuhaHtcra47G9ZdLFWICrTgPdMDI=; b=T4flrGs3CFHnAQVvGhmPpcorioKPHnHnS88vv0gYbUzPTI/xy6skqt/+8Kk7xLl0I2 3xs/O8twd73HbVCQqWtnwMjaFCPnp87+lr1j474tdi8nJ9BuxLDq4OGrEtojkGroF1AK unNjQjSSApdxJs2SGgDXW34vvcw0DT9HFwDLoiGrsBlzKaRmbUdU7Tfnz8ZN9KLsHtm7 jOb5iZbBAI0LrqeD93XWYuz27P2vFm8wmf1Zytri1id3J+g6DMcaMgqbRw14Z7i7W40+ es0atGKBb2+DxBgOx9H244OyA8criOh0PfaB0BYPzrUrKTdiqGv3Nj/tD7n+N8tWUqGs NmXQ== X-Gm-Message-State: AJIora8hRQh4XTkLW/T1FophWBVKKQMvjO24QCz4SnqoAy2hml0z6k8b o6lDzIQfYZf1KG9i7aB7NtiA1DIT/ObNI3LIXi3pcyAWYkf5CUp18UMdN01vU93Ijy1uhhKmKYG PVsQzNqya1hl/htJxGdezoSt17bt7 X-Received: by 2002:adf:ffcf:0:b0:21a:3cc0:d624 with SMTP id x15-20020adfffcf000000b0021a3cc0d624mr23496577wrs.164.1655814327321; Tue, 21 Jun 2022 05:25:27 -0700 (PDT) X-Google-Smtp-Source: AGRyM1vHTlAgCbYSPwKOnD4wThbGsJJ+9XZS//2sA4ocZl1PpUmbJFPrznizqZ5xjm3YK7dzwI4CFQ== X-Received: by 2002:adf:ffcf:0:b0:21a:3cc0:d624 with SMTP id x15-20020adfffcf000000b0021a3cc0d624mr23496546wrs.164.1655814327013; Tue, 21 Jun 2022 05:25:27 -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 b5-20020a05600c4e0500b0039aef592ca0sm18064551wmq.35.2022.06.21.05.25.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jun 2022 05:25:26 -0700 (PDT) Message-ID: <643c44e7-48be-375b-c7ab-6a30b5ee2937@redhat.com> Date: Tue, 21 Jun 2022 14:25:25 +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: Alistair Popple 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> <34e94bdb-675a-5d5c-6137-8aa1ee658d49@redhat.com> <87letq6wb5.fsf@nvdebian.thelocal> From: David Hildenbrand Organization: Red Hat In-Reply-To: <87letq6wb5.fsf@nvdebian.thelocal> 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: "Sierra Guiza, Alejandro \(Alex\)" , rcampbell@nvidia.com, willy@infradead.org, Felix Kuehling , amd-gfx@lists.freedesktop.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org, jglisse@redhat.com, dri-devel@lists.freedesktop.org, jgg@nvidia.com, 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 13:55, Alistair Popple wrote: > > David Hildenbrand writes: > >> 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(). > > Ugh, I think you might be right about try_grab_folio(). > > We didn't update folio_is_pinnable() to include device coherent pages > because device coherent pages are pinnable. It is really just > FOLL_LONGTERM that we want to prevent here. > > For normal PUP that is done by my change in > check_and_migrate_movable_pages() which migrates pages being pinned with > FOLL_LONGTERM. But I think I incorrectly assumed we would take the > pte_devmap() path in gup_pte_range(), which we don't for coherent pages. > So I think the check in try_grab_folio() needs to be: I think I said it already (and I might be wrong without reading the code), but folio_is_pinnable() is *only* called for long-term pinnings. It should actually be called folio_is_longterm_pinnable(). That's where that check should go, no? -- Thanks, David / dhildenb