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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 1/2] mm/huge_memory: use folio's memcg inside __folio_split() Message-ID: 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260730-add-gfp_account-to-xas_split_alloc-v2-1-5a56c2361d85@nvidia.com> X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: C038E4000B X-Stat-Signature: 85r3q6r9ctkocxxq9pfg9bdp4id11gfq X-HE-Tag: 1785576987-765291 X-HE-Meta: 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 t/taRlA9 ftheMju0T4EGXjXlr4lcJ4OGmDSDDNs+TGf1aD3/xxBM3UcgSyaCX0/xVkWL9iQ08ZstZPz5ktwJTjXXkLZeH+J0D8zPY9BfnbCkVriBAh5uoVVWraUY6486HD2NCqtph7xXy7beJ7/2dGlJ/G2x8AwfsBahArVIJpKipG5NGwqIQtjyw/Htn4qs+lV/1YJrLPCXMEM60FLxqdnXnA/hZNhQkXkm+8XE33E9ZB5UWI/EwBTIAUf72W9UG1YZhiXDFA3lUWMe3/tOm4+7vV38dSrydxzzZOmUFlF690XoIHnjxIH+8+01ZqyMU5N/AVnNNPAsRejMy7CZslKcNnjwNDGvzkHLQdTbIGf5dCOPtN1satEo4999xWvdy9uwRKdPeHW64xKB3pcDEhFE3cO9n59F8SA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jul 30, 2026 at 10:18:00PM -0400, Zi Yan wrote: > During a pagecache folio split, an xarray node allocation can happen and > needs to charge at folio's memcg instead of folio split invoker's memcg, > because for example folio split can happen during reclaim and reclaim's > active memcg might not be folio's memcg. Switch to folio's memcg at the > beginning and switch back afterwards. I assume this is the only allocation? I guess in general it makes sense 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? > 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 = folio_next(folio); > bool is_anon = folio_test_anon(folio); > + struct mem_cgroup *memcg, *old_memcg; > struct address_space *mapping = NULL; > struct anon_vma *anon_vma = NULL; > int old_order = folio_order(folio); > struct folio *new_folio, *next; > int nr_shmem_dropped = 0; > enum ttu_flags ttu_flags = 0; > - int ret; > pgoff_t end = 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 != page_folio(split_at) || folio != page_folio(lock_at)) { > ret = -EINVAL; > - goto out; > + goto out_no_memcg; > } > > if (new_order >= old_order) { > ret = -EINVAL; > - goto out; > + goto out_no_memcg; > } > > ret = folio_check_splittable(folio, new_order, split_type); > if (ret) { > VM_WARN_ONCE(ret == -EINVAL, "Tried to split an unsplittable folio"); > - goto out; > + goto out_no_memcg; This function really badly needs splitting up and probably some cleanup.h work :) > } > > + /* > + * switch to folio's memcg as xarray node allocation can happen and > + * needs to charge to it. > + */ > + memcg = get_mem_cgroup_from_folio(folio); > + old_memcg = set_active_memcg(memcg); > + > if (is_anon) { > /* > * The caller does not necessarily hold an mmap_lock that would > @@ -4231,6 +4239,10 @@ static int __folio_split(struct folio *folio, unsigned int new_order, > if (mapping) > i_mmap_unlock_read(mapping); > out: > + /* restore to caller's old_memcg */ > + set_active_memcg(old_memcg); > + mem_cgroup_put(memcg); > +out_no_memcg: > xas_destroy(&xas); > if (is_pmd_order(old_order)) > count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED); > > -- > 2.53.0 > -- Cheers, Lorenzo