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[2003:cb:c70c:e700:4d5c:81e2:253e:e397]) by smtp.gmail.com with ESMTPSA id j7-20020adfea47000000b00317731a6e07sm19508032wrn.62.2023.08.23.08.17.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Aug 2023 08:17:38 -0700 (PDT) Message-ID: Date: Wed, 23 Aug 2023 17:17:37 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH mm-unstable v1 1/4] mm/swap: stop using page->private on tail pages for THP_SWAP To: Yosry Ahmed Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, Andrew Morton , Matthew Wilcox , Peter Xu , Catalin Marinas , Will Deacon , Hugh Dickins , Seth Jennings , Dan Streetman , Vitaly Wool References: <20230821160849.531668-1-david@redhat.com> <20230821160849.531668-2-david@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 5D088100013 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: bxe36fnidxejrae7wy397q64is4xazxm X-HE-Tag: 1692803862-311427 X-HE-Meta: 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 G4Z9xz2/ 5GeJ/+jfurzykbh7yhKpt2fYCxDRheA9mzbEr+Pl5nd+AuPt4GsPZUwZgp2+IAYY43DSH3DWZ/0SZqZYnKrhzWfScaXCtUoNSuWYy0k0Yhp4zw/XGquv8PIL5lUWmyU8L919Iv4WYpcrPTiLqs7Yj0vi14EEoUDyYMuQgv1nVGF6aGWNVbm3AlUF8nyVaDmeaYJWegvugWCmdOR88wT4EVpJpWxnbzt0DjoPXYBSTpCPPSzBU8wmBM7pg0KJJdX+sY5vyCCr/LF6fnsyIYbRuH/2uZM60hQIzFP2mCzB1MCJsMSRTk0KlLqfzz3co/srPXGHPJ8zcf/3pRbQgREcmXuIpsVPkmeG7ZjqdsC8SATp7lqrltOdX5VKmPvSVtF/KJHpM 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 23.08.23 17:12, Yosry Ahmed wrote: > On Mon, Aug 21, 2023 at 9:09 AM David Hildenbrand wrote: >> >> Let's stop using page->private on tail pages, making it possible to >> just unconditionally reuse that field in the tail pages of large folios. >> >> The remaining usage of the private field for THP_SWAP is in the THP >> splitting code (mm/huge_memory.c), that we'll handle separately later. >> >> Update the THP_SWAP documentation and sanity checks in mm_types.h and >> __split_huge_page_tail(). >> >> Signed-off-by: David Hildenbrand > > The mm part looks good to me (with the added fixup): > > Reviewed-by: Yosry Ahmed Thanks! >> /** >> diff --git a/include/linux/swap.h b/include/linux/swap.h >> index bb5adc604144..84fe0e94f5cd 100644 >> --- a/include/linux/swap.h >> +++ b/include/linux/swap.h >> @@ -339,6 +339,15 @@ static inline swp_entry_t folio_swap_entry(struct folio *folio) >> return entry; >> } >> >> +static inline swp_entry_t page_swap_entry(struct page *page) >> +{ >> + struct folio *folio = page_folio(page); >> + swp_entry_t entry = folio_swap_entry(folio); >> + >> + entry.val += page - &folio->page; >> + return entry; >> +} >> + >> static inline void folio_set_swap_entry(struct folio *folio, swp_entry_t entry) >> { >> folio->private = (void *)entry.val; >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index cc2f65f8cc62..c04702ae71d2 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -2446,18 +2446,15 @@ static void __split_huge_page_tail(struct page *head, int tail, >> page_tail->index = head->index + tail; >> >> /* >> - * page->private should not be set in tail pages with the exception >> - * of swap cache pages that store the swp_entry_t in tail pages. >> - * Fix up and warn once if private is unexpectedly set. >> - * >> - * What of 32-bit systems, on which folio->_pincount overlays >> - * head[1].private? No problem: THP_SWAP is not enabled on 32-bit, and >> - * pincount must be 0 for folio_ref_freeze() to have succeeded. >> + * page->private should not be set in tail pages. Fix up and warn once >> + * if private is unexpectedly set. >> */ >> - if (!folio_test_swapcache(page_folio(head))) { >> - VM_WARN_ON_ONCE_PAGE(page_tail->private != 0, page_tail); >> + if (unlikely(page_tail->private)) { >> + VM_WARN_ON_ONCE_PAGE(true, page_tail); >> page_tail->private = 0; >> } > > Could probably save a couple of lines here: > > if (VM_WARN_ON_ONCE_PAGE(page_tail->private != 0, page_tail)) > > page_tail->private = 0; > That would mean that we eventually compile out the runtime check #define VM_WARN_ON_ONCE_PAGE(cond, page) BUILD_BUG_ON_INVALID(cond) -- Cheers, David / dhildenb