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[2003:cb:c70a:7e00:bb5b:b526:5b76:5824]) by smtp.gmail.com with ESMTPSA id x24-20020a7bc218000000b003942a244ee7sm6509031wmi.44.2022.06.17.14.19.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Jun 2022 14:19:52 -0700 (PDT) Message-ID: <6aef4b7f-0ced-08cd-1f0c-50c22996aa41@redhat.com> Date: Fri, 17 Jun 2022 23:19:50 +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: "Sierra Guiza, Alejandro (Alex)" , jgg@nvidia.com Cc: Felix.Kuehling@amd.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, 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> From: David Hildenbrand Organization: Red Hat In-Reply-To: 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 ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655500799; a=rsa-sha256; cv=none; b=5wjkevhUZ4T063c/8YwhTDAZFKkVgRqdpA0PT/VufFlyf00krOv612lwfT0NxwhjbIgjSp gf0fR4C4mynAglyJcIpyjhy5pEWCVQ8a7JCK7r4Ea9CPBiFbYJWhkJsZ55vblhItv2DyIc R/w8xdMbpWdTOk5GfdlOsg/SGDJSWpU= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=LnLO1Svs; spf=none (imf04.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655500799; h=from:from:sender: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:dkim-signature; bh=Azo6PZsDvSmIPxJaSSgXZfKMrP2WPlFn0BkwBvhAsds=; b=Dq+yBXTpIDzOVyWCnw9f+pabZgRlQBfmpW1ZCUiGuWxIo3+ZYKaYTQyniC6DzgYD7Btxbh xn3+pGSYIPK4FxmXsw2iOOLA1+RyAPIUqkZY3Yde4pVAZRmBuabVH70m0efCCv6NC7ZjSO aGVVXhn35XTZD78edwJdvc1NgQrhOPo= X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0E75A40090 X-Stat-Signature: wjoriroqp6gsrtt5wb74b1brj6fiffu9 Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=LnLO1Svs; spf=none (imf04.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspam-User: X-HE-Tag: 1655500798-547418 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: 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? I am probably missing something important. -- Thanks, David / dhildenb