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Shutemov\"" , =?utf-8?q?=22Michal_Koutn=C3=BD=22?= , Roman Gushchin , "\"Zach O'Keefe\"" , Hugh Dickins , Mcgrof Chamberlain , Andrew Morton , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v4 0/7] Split a folio to any lower order folios Date: Wed, 14 Feb 2024 11:35:50 -0500 X-Mailer: MailMate (1.14r6018) Message-ID: <3D59E86D-0B66-4829-AE33-280317F913D8@nvidia.com> In-Reply-To: <46f61262-e197-456c-97f1-d464ad5688c1@redhat.com> References: <20240213215520.1048625-1-zi.yan@sent.com> <659e1abb-40d0-42ba-ba0a-8256d7eb1c5a@redhat.com> <66d4b27f-85e4-458e-8d66-54f800c5c65f@arm.com> <46f61262-e197-456c-97f1-d464ad5688c1@redhat.com> Content-Type: multipart/signed; boundary="=_MailMate_F12DAB28-7693-40ED-B067-53D889A5D109_="; micalg=pgp-sha512; protocol="application/pgp-signature" X-ClientProxiedBy: BL1PR13CA0338.namprd13.prod.outlook.com (2603:10b6:208:2c6::13) To DS7PR12MB5744.namprd12.prod.outlook.com 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X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 0zxIAs04AC+DjKeMG9MgB1g7Pf0rkzzA9OYKtTjtUgSf5xFOAsp3qPtJUM6XwUNI X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW5PR12MB5682 X-Rspamd-Queue-Id: C5C7F100023 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: m5d49usxkrn9spmi7tre1b96u8jq98wy X-HE-Tag: 1707928559-866810 X-HE-Meta: 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 OkXRwPK5 JMJ4nlqHaphNqyPubVJaHGjO6LPgPSXa6dEBx54rUjP5+1w6BAfMhVn6WCo3H1CGjZPKMlNu0Bqznv4YllBUJvYqLPCn5uaNR9nlcr4ZUkKHApLF8YxkxcIsn0mnqTzAaZMJI0GzD8GL7/TlDRrHXT+QzgldYmcXWr+faKJH03IkwHQONbvaBZeap+or4/9JSICKXaZNbgAZc2tAYDTt/tyuEIUwYyXadZ3HeqzSz1kwhKwKq7HPREKPw/pI0aFvSb2M7C5Byix6tWE1jqjm4ckCMhho+f1XavGm454XkIIqIrW4L6Yq6uNoX3gZ6kd/WbkWmWHc8tibn03hFluS+tX8Erb8tr8hCxbrb8oDn3qybEOI= 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: List-Subscribe: List-Unsubscribe: --=_MailMate_F12DAB28-7693-40ED-B067-53D889A5D109_= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On 14 Feb 2024, at 5:55, David Hildenbrand wrote: > On 14.02.24 11:50, Ryan Roberts wrote: >> On 13/02/2024 22:31, Zi Yan wrote: >>> On 13 Feb 2024, at 17:21, David Hildenbrand wrote: >>> >>>> On 13.02.24 22:55, Zi Yan wrote: >>>>> From: Zi Yan >>>>> >>>>> Hi all, >>>>> >>>>> File folio supports any order and multi-size THP is upstreamed[1], = so both >>>>> file and anonymous folios can be >0 order. Currently, split_huge_pa= ge() >>>>> only splits a huge page to order-0 pages, but splitting to orders h= igher than >>>>> 0 is going to better utilize large folios. In addition, Large Block= >>>>> Sizes in XFS support would benefit from it[2]. This patchset adds s= upport for >>>>> splitting a large folio to any lower order folios and uses it durin= g file >>>>> folio truncate operations. >>>>> >>>>> For Patch 6, Hugh did not like my approach to minimize the number o= f >>>>> folios for truncate[3]. I would like to get more feedback, especial= ly >>>>> from FS people, on it to decide whether to keep it or not. >>>> >>>> I'm curious, would it make sense to exclude the "more" controversial= parts (i.e., patch #6) for now, and focus on the XFS use case only? >>> >>> Sure. Patch 6 was there to make use of split_huge_page_to_list_to_ord= er(). >>> Now we have multi-size THP and XFS use cases, it can be dropped. >> >> What are your plans for how to determine when to split THP and to what= order? I >> don't see anything in this series that would split anon THP to non-zer= o order? >> >> We have talked about using hints from user space in the past (e.g. mr= emap, >> munmap, madvise, etc). But chrome has a use case where it temporarily = mprotects >> a single (4K) page as part of garbage collection (IIRC). If you eagerl= y split on >> that hint, you will have lost the benefits of the large folio when it = later >> mprotects back to the original setting. > > Not only that, splitting will make some of these operations more expens= ive, possibly with no actual benefit. > >> >> I guess David will suggest this would be a good use case for the khuge= paged-lite >> machanism we have been talking about. I dunno - it seems wasteful to s= plit then >> collapse again. > > I agree. mprotect() and even madvise(), ... might not be good candidate= s for splitting. mremap() likely is, if the folio is mapped exclusively. = MADV_DONTNEED/munmap()/mlock() might be good candidates (again, if mapped= exclusively). This will need a lot of thought I'm afraid (as you say, de= ferred splitting is another example). My initial use was for splitting 1GB THP to 2MB THP, but 1GB THP is not u= pstream yet. So for now, this might only be used by XFS. For anonymous large foli= os, we will use this when we find a justified use case. What I can think of i= s when a PMD-mapped THP happens to be split and the resulting order can be = a HW/SW favored order, like 64KB or 32KB (to be able to use contig PTE), we split= to that order, otherwise, we still split to order-0. -- Best Regards, Yan, Zi --=_MailMate_F12DAB28-7693-40ED-B067-53D889A5D109_= Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQJDBAEBCgAtFiEE6rR4j8RuQ2XmaZol4n+egRQHKFQFAmXM6+cPHHppeUBudmlk aWEuY29tAAoJEOJ/noEUByhUVosP/0Fd8rJzrwcJQR1fD6IRLWQ2HLeASzM37Uec 5aSfg9tHn9hsNzYXmwaLcJhYjBRWWQ+9SBAfG+pdeYtudAxmOhmBECuf6evnE6uS Obx4+f6xgXU19SiKe60q1OijOjIS2VAVcItGjA327xVkJ9vniPWYj4Wv0nRYcGaF S0+z9I/H/7FkW+Tz9VVCYJqC/zDaWyMlImacY3ccX8OvNyiRiLwDI/R8G1jKRFt/ HghzYcPNlPRF2vgiW3fKR6Hrpy4Vo/nZs+0N5JPCNbQY/KHDx2Uc+bZbZetGFqak 4a63k/J3bAcaoRx1pFZeSWRxT1fpjHx0/r5EmCx/lmI78Zsz/HAzllEgAa5m4U+d S3BST4m3SFpAEBc0oEIIzhr2S+ZRCHAQ7WiRYYtxiLiuDIoG+yA78qvUbHG3duIa tt+ixRtryYyBidios+X0deLt+AVxsEfQA5ASy7mp4c7wZ7/E6b9dnQLD0YRhQ0Vt ehguEnv7xtusxQQFS4Qc0wZrqWalkH9Z7beTFRFi3sD1+DZKY64vCoVCoWgSMBo6 R9xRyTk3xSHhLwR23xnQ1RG7FNWLoLa/qhxploO745CkgUD72hdolFSgii1x6rpf jOgAGi3XHRhaFM//LOW9aVFKIOjVIEIBuT62Yu1p7ltuCi6DjJYEutbB9BCpDKKQ S2Z7WO/a =z7b4 -----END PGP SIGNATURE----- --=_MailMate_F12DAB28-7693-40ED-B067-53D889A5D109_=--