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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 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> 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=1655811127; a=rsa-sha256; cv=none; b=HeAH2rl/+9oaFPaHjM2Yk8XyOCTc7GAKZmzEPAL9JbwBRtDR77TrraG5cEQTIhI2WUSdNW gU/F2TAi6C97HWPuhPkTFgZ+R6LQBDklyFvwe/g0ovEG4pmlPHabJ9RVdND3rWBNJxOdfc f4kVXY/ET+jCDQKMvTgSha2SK4ZZe3U= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655811127; 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=Y1o/jnMsU4IPX6HlOfyZ4A2cxwPbVUo4lnU9g11rsaY=; b=mDZyPP0oV/EVzPrzSCX40mhiYBwqg71Bml7yjVdwI4LDQ8JTq0m85jn05DfKkHTE1RKuPg XITXVvv80AZ5Q7rP5m8q2VTcnLga3EIjii70vHRKu5WvsI9u6INVBWmpbLOkpPPYAEWqNt Fh7/yH6KTRrjPGVQCSvuFWpg1M8OAGM= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=AVky9HMF; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf20.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=AVky9HMF; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf20.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 1E3041C0021 X-Stat-Signature: 5h8t4ixijz9nmh3q6863yyruzjybdtye X-HE-Tag: 1655811126-224430 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 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