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Wed, 23 Aug 2023 08:21:38 -0700 (PDT) MIME-Version: 1.0 References: <20230821160849.531668-1-david@redhat.com> <20230821160849.531668-2-david@redhat.com> In-Reply-To: From: Yosry Ahmed Date: Wed, 23 Aug 2023 08:21:01 -0700 Message-ID: Subject: Re: [PATCH mm-unstable v1 1/4] mm/swap: stop using page->private on tail pages for THP_SWAP To: David Hildenbrand 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: 6xegjzjsf189nco5cgxqzxcry4hqe6af X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A4B54140010 X-HE-Tag: 1692804099-33483 X-HE-Meta: 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 fqs81NID 4or1h6GUiMJs+TcOMA3ZoRMMG9iWZXjH+/o3pbVO0C5WFZQHb9kRjNrDigNM3PC6Fn46ThI/1cvbUnL1SyYFe1MWM9oECMvJ4XX1DDRu9Nven2Ih/L5uzvt97XIT930j/zaG+By3dzijlkDjMffJNwZkrOaDaMlgHevBZyKe19s0/ulXBNsb1/R4vURHNSBqyLx5M2XI/Ca6miZ9Mhnh72bgAQ8pJOAnE0SRYldEKcFRhJ1UdEpuDQsippStjuDW6d00mU1RWV51Ss5Y0gpPxFc2hD+r9cTn1YFbG0DdArDIwEOWgjrrFaNG7EDVa+w11cXm2 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 Wed, Aug 23, 2023 at 8:17=E2=80=AFAM David Hildenbrand wrote: > > On 23.08.23 17:12, Yosry Ahmed wrote: > > On Mon, Aug 21, 2023 at 9:09=E2=80=AFAM 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 folio= s. > >> > >> 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 =3D page_folio(page); > >> + swp_entry_t entry =3D folio_swap_entry(folio); > >> + > >> + entry.val +=3D page - &folio->page; > >> + return entry; > >> +} > >> + > >> static inline void folio_set_swap_entry(struct folio *folio, swp_ent= ry_t entry) > >> { > >> folio->private =3D (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 =3D head->index + tail; > >> > >> /* > >> - * page->private should not be set in tail pages with the exce= ption > >> - * of swap cache pages that store the swp_entry_t in tail page= s. > >> - * 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 w= arn once > >> + * if private is unexpectedly set. > >> */ > >> - if (!folio_test_swapcache(page_folio(head))) { > >> - VM_WARN_ON_ONCE_PAGE(page_tail->private !=3D 0, page_t= ail); > >> + if (unlikely(page_tail->private)) { > >> + VM_WARN_ON_ONCE_PAGE(true, page_tail); > >> page_tail->private =3D 0; > >> } > > > > Could probably save a couple of lines here: > > > > if (VM_WARN_ON_ONCE_PAGE(page_tail->private !=3D 0, page_tail)) > > > > page_tail->private =3D 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) I thought the warning would be compiled out but not the check, my bad. > > -- > Cheers, > > David / dhildenb >