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Shutemov" , "Matthew Wilcox (Oracle)" , Ryan Roberts , Hugh Dickins , Yang Shi , Miaohe Lin , Kefeng Wang , Yu Zhao , John Hubbard , linux-kernel@vger.kernel.org Subject: Re: [PATCH RESEND v3 6/9] mm/truncate: use folio_split() for truncate operation. 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0g0155kIyNoLFLkJD5RE2hSlkq9mSwrPc/gARh78piJ5DHhn3uxz9IiwjqZgA42+TEmsuU8DYo+hJByA2Qq26LiOqaii12VMyVJAQ7Fw6q6gLzjmYhyi2JGdFlcJJQkXmvOZ3Ms+4PA95mjXZvya5uuP/aKyVlwCqLQYSGuUOYPl1VuYwmstdYxZMcp1uVeQLc3DP1vmkrP+cghLxnKj0bJQu6TaohN1wvKL51qWEOGwZvtfFoiN/Ti9mvBvQtq3GT+sHPCQE029ai+mO82DAwqU8RwLHZIxzZXEn4UWIhBNZ0bAYmiSTaaujQv4kg65upgXR3MYGdeafRTdQcM0VsjuLXpd4KA+FGrdLC1Ehof4w+20= 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: On 10 Dec 2024, at 15:41, Zi Yan wrote: > On 10 Dec 2024, at 15:12, David Hildenbrand wrote: > >> On 05.12.24 01:18, Zi Yan wrote: >>> Instead of splitting the large folio uniformly during truncation, use= >>> buddy allocator like split at the start of truncation range to minimi= ze >>> the number of resulting folios. >>> >>> For example, to truncate a order-4 folio >>> [0, 1, 2, 3, 4, 5, ..., 15] >>> between [3, 10] (inclusive), folio_split() splits the folio to >>> [0,1], [2], [3], [4..7], [8..15] and [3], [4..7] can be dropped and >>> [8..15] is kept with zeros in [8..10]. >> >> But isn't that making things worse that they are today? Imagine falloc= ate() on a shmem file where we won't be freeing memory? > > You mean [8..10] are kept? Yes, it is worse. And the solution would be > split at both 3 and 10. For now folio_split() returns -EINVAL for > shmem mappings, but that means I have a bug in this patch. The newly ad= ded > split_folio_at() needs to retry uniform split if buddy allocator like > split returns with -EINVAL, otherwise, shmem truncate will no longer > split folios after this patch. > > Thank you for checking the patch. I will fix it in the next version. I am going to add two functions: split_huge_page_supported(folio, new_ord= er) and folio_split_support(folio, new_order) to perform the order and folio-= >mapping checks at the beginning of __folio_split(). So truncate and other potenti= al callers can make the right function call. Best Regards, Yan, Zi