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Howlett" , "Nico Pache" , "Ryan Roberts" , "Dev Jain" , "Barry Song" , "Lance Yang" , "Usama Arif" , , , To: "Lorenzo Stoakes (ARM)" From: "Zi Yan" Subject: Re: [PATCH v2 1/2] mm/huge_memory: use folio's memcg inside __folio_split() X-Mailer: aerc 0.21.0 References: <20260730-add-gfp_account-to-xas_split_alloc-v2-0-5a56c2361d85@nvidia.com> <20260730-add-gfp_account-to-xas_split_alloc-v2-1-5a56c2361d85@nvidia.com> In-Reply-To: X-ClientProxiedBy: BLAPR05CA0021.namprd05.prod.outlook.com (2603:10b6:208:36e::17) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|BL4PR12MB9484:EE_ X-MS-Office365-Filtering-Correlation-Id: 3d2250a7-4c63-42f6-2280-08def17332bd X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|1800799024|366016|376014|7416014|11063799006|56012099006|4143699003|5023799004|6133799003|10067099003|18002099003|22082099003; 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Switch to folio's memcg at t= he >> >> beginning and switch back afterwards. >> > >> > I assume this is the only allocation? I guess in general it makes sens= e to have >> > the folio's memcg be active here regardless. >> > >> >> >> >> Suggested-by: Johannes Weiner >> >> Fixes: 6b24ca4a1a8d4 ("mm: Use multi-index entries in the page cache"= ) >> > >> > Cc: stable? >> >> Like you said above, only xas_split_alloc() is affected. And we have not >> seen related workingset regression report (like what Johannes reported >> in commit 7b785645e8f13 ("mm: fix page cache convergence regression")). >> It might be OK to not backport. >> >> Johannes, what is your take on this? >> >> > >> >> Signed-off-by: Zi Yan >> > >> > Change seems reasonable overall. >> > >> > Acked-by: Lorenzo Stoakes (ARM) >> > >> >> --- >> >> mm/huge_memory.c | 20 ++++++++++++++++---- >> >> 1 file changed, 16 insertions(+), 4 deletions(-) >> >> >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> >> index 04e8a6b553435..b9c2d8908e564 100644 >> >> --- a/mm/huge_memory.c >> >> +++ b/mm/huge_memory.c >> >> @@ -4063,34 +4063,42 @@ static int __folio_split(struct folio *folio,= unsigned int new_order, >> >> XA_STATE(xas, &folio->mapping->i_pages, folio->index); >> >> struct folio *end_folio =3D folio_next(folio); >> >> bool is_anon =3D folio_test_anon(folio); >> >> + struct mem_cgroup *memcg, *old_memcg; >> >> struct address_space *mapping =3D NULL; >> >> struct anon_vma *anon_vma =3D NULL; >> >> int old_order =3D folio_order(folio); >> >> struct folio *new_folio, *next; >> >> int nr_shmem_dropped =3D 0; >> >> enum ttu_flags ttu_flags =3D 0; >> >> - int ret; >> >> pgoff_t end =3D 0; >> >> + int ret; >> >> >> >> VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); >> >> VM_WARN_ON_ONCE_FOLIO(!folio_test_large(folio), folio); >> >> >> >> if (folio !=3D page_folio(split_at) || folio !=3D page_folio(lock_a= t)) { >> >> ret =3D -EINVAL; >> >> - goto out; >> >> + goto out_no_memcg; >> >> } >> >> >> >> if (new_order >=3D old_order) { >> >> ret =3D -EINVAL; >> >> - goto out; >> >> + goto out_no_memcg; >> >> } >> >> >> >> ret =3D folio_check_splittable(folio, new_order, split_type); >> >> if (ret) { >> >> VM_WARN_ONCE(ret =3D=3D -EINVAL, "Tried to split an unsplittable f= olio"); >> >> - goto out; >> >> + goto out_no_memcg; >> > >> > This function really badly needs splitting up and probably some cleanu= p.h work :) >> >> You mean folio_check_splittable()? You want to move -EINVAL checks a >> separate one? > > No __folio_split(). > > Comment about cleanup.h really was the whole pattern of goto xxx for vari= ous > levels of unwinding things. > > But really I mean the folio splitting code in general, there's a lot of > massive-complicated-functions with a million things going on at once, > __folio_freeze_and_split_unmapped() is another. > > Feels like we should really have this stuff in something like mm/folio.c = anyway > too now that's renamed :) > I agree that __folio_split() is handling multiple cases, anon, shmem, pagecache, all together. Do you prefer: 1. split __folio_split() to handle each case in a separate function with some code duplication, like xarray for pagecache and shmem, freeze/unfreeze folio for all;=20 or 2. encapulate per-case code in small functions, like if (is_anon) split_prepare_anon(); else split_prepare_file_backed(); __folio_freeze_and_split_unmapped(); if (is_anon) post_split_anon(); else post_split_file_backed(); --=20 Best Regards, Yan, Zi