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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , Ralph Campbell , Mika =?iso-8859-1?Q?Penttil=E4?= , Matthew Brost , Francois Dugast Subject: Re: [PATCH] mm/huge_memory.c: introduce folio_split_unmapped Message-ID: <20251114032105.sdkjaoiwpdmpynew@master> Reply-To: Wei Yang References: <20251114012228.2634882-1-balbirs@nvidia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251114012228.2634882-1-balbirs@nvidia.com> User-Agent: NeoMutt/20170113 (1.7.2) On Fri, Nov 14, 2025 at 12:22:28PM +1100, Balbir Singh wrote: [...] >@@ -4079,6 +4091,36 @@ static int __folio_split(struct folio *folio, unsigned int new_order, > return ret; > } > >+/* >+ * This function is a helper for splitting folios that have already been unmapped. >+ * The use case is that the device or the CPU can refuse to migrate THP pages in >+ * the middle of migration, due to allocation issues on either side >+ * >+ * The high level code is copied from __folio_split, since the pages are anonymous >+ * and are already isolated from the LRU, the code has been simplified to not >+ * burden __folio_split with unmapped sprinkled into the code. >+ * >+ * None of the split folios are unlocked >+ */ >+int folio_split_unmapped(struct folio *folio, unsigned int new_order) >+{ >+ int extra_pins, ret = 0; >+ >+ VM_WARN_ON_FOLIO(folio_mapped(folio), folio); >+ VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); >+ VM_WARN_ON_ONCE_FOLIO(!folio_test_large(folio), folio); >+ Compared with original logic, we did check folio_split_supported() and check whether new_order is supported for the file system. Currently folio_split_unmapped() only pass 0 as new_order, which looks good. But for a generic helper, it looks reasonable to do the check, IMHO. >+ if (!can_split_folio(folio, 1, &extra_pins)) >+ return -EAGAIN; >+ >+ local_irq_disable(); >+ ret = __folio_freeze_and_split_unmapped(folio, new_order, &folio->page, NULL, >+ NULL, false, NULL, SPLIT_TYPE_UNIFORM, >+ 0, extra_pins); >+ local_irq_enable(); >+ return ret; >+} >+ > /* > * This function splits a large folio into smaller folios of order @new_order. > * @page can point to any page of the large folio to split. The split operation -- Wei Yang Help you, Help me