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([2a02:6b6a:b465:0:bbb6:1437:eebd:d9ef]) by smtp.gmail.com with ESMTPSA id x1-20020a5d54c1000000b003176f2d9ce5sm18648471wrv.71.2023.08.02.03.06.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 02 Aug 2023 03:06:50 -0700 (PDT) Message-ID: <24ed8a1f-2134-6082-7bc9-f8662dc723bd@bytedance.com> Date: Wed, 2 Aug 2023 11:06:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2 Subject: Re: [External] Re: [v2 1/6] mm: hugetlb: Skip prep of tail pages when HVO is enabled Content-Language: en-US To: Muchun Song Cc: linux-kernel@vger.kernel.org, fam.zheng@bytedance.com, liangma@liangbit.com, simon.evans@bytedance.com, punit.agrawal@bytedance.com, linux-mm@kvack.org, mike.kravetz@oracle.com, rppt@kernel.org References: <20230730151606.2871391-1-usama.arif@bytedance.com> <20230730151606.2871391-2-usama.arif@bytedance.com> From: Usama Arif In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 7E6C6A0004 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: ozh4m7tbwz65fxagn6jpnyx3nj9t1bsi X-HE-Tag: 1690970812-866471 X-HE-Meta: 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 DCdMPboN MvL4hGh8/vidq8elBq2Xby5NqQkSfWXWYakoPqbIB8CLd1DIVEjRyXQxOoKex+qRGtSrigbZd9SyyAQTsS8oRZWjgdFq0Ycaxe12ytG1ZLhAa16/ILBa/F6arwgMqZ3sbV0EFfh1VGfzHv53+wFLFG6wauzcp1gYQJSFIH0DdvRnGQlBNrVz1wPFOPv2boVM/RoelVEMtBBwMYi45QkP3GeUvEQ1rbdWnPNgHZ6uNb40MHjZXgssiExCsXgo8CCL/YjuMd0lv9o4UluPL4y1jLIcq71vCCVGNMX2Jq2J7p0199EMyFTdUV/T8sG62XBkD6qSyd/BUvVaTkSDeTpBboaP5Wgb00ZKekuXMK0GvTpiYdENx/qBlJ/qGatKRWiTqjVG/yQ5R4PWkCTAHeJQUjIu+VLYdNBIlJZKVlb7a1DzXBfQzTKwX4JLBTg== 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: On 01/08/2023 03:04, Muchun Song wrote: > > > On 2023/7/30 23:16, Usama Arif wrote: >> When vmemmap is optimizable, it will free all the duplicated tail >> pages in hugetlb_vmemmap_optimize while preparing the new hugepage. >> Hence, there is no need to prepare them. >> >> For 1G x86 hugepages, it avoids preparing >> 262144 - 64 = 262080 struct pages per hugepage. >> >> The indirection of using __prep_compound_gigantic_folio is also removed, >> as it just creates extra functions to indicate demote which can be done >> with the argument. >> >> Signed-off-by: Usama Arif >> --- >>   mm/hugetlb.c         | 32 ++++++++++++++------------------ >>   mm/hugetlb_vmemmap.c |  2 +- >>   mm/hugetlb_vmemmap.h | 15 +++++++++++---- >>   3 files changed, 26 insertions(+), 23 deletions(-) >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index 64a3239b6407..541c07b6d60f 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -1942,14 +1942,23 @@ static void prep_new_hugetlb_folio(struct >> hstate *h, struct folio *folio, int ni >>       spin_unlock_irq(&hugetlb_lock); >>   } >> -static bool __prep_compound_gigantic_folio(struct folio *folio, >> -                    unsigned int order, bool demote) >> +static bool prep_compound_gigantic_folio(struct folio *folio, struct >> hstate *h, bool demote) >>   { >>       int i, j; >> +    int order = huge_page_order(h); >>       int nr_pages = 1 << order; >>       struct page *p; >>       __folio_clear_reserved(folio); >> + >> +    /* >> +     * No need to prep pages that will be freed later by >> hugetlb_vmemmap_optimize. >> +     * Hence, reduce nr_pages to the pages that will be kept. >> +     */ >> +    if (IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP) && >> +            vmemmap_should_optimize(h, &folio->page)) >> +        nr_pages = HUGETLB_VMEMMAP_RESERVE_SIZE / sizeof(struct page); > > We need to initialize the refcount to zero of tail pages (see the big > comment below in this function), given a situation that someone (maybe > GUP) could get a ref on the tail pages when the vmemmap is optimizing, > what prevent this from happening? > > Thanks. > Thanks for pointing this out, will limit to boot time for solving this in next version.