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Thu, 21 Mar 2024 01:42:49 -0700 (PDT) MIME-Version: 1.0 References: <20240304081348.197341-1-21cnbao@gmail.com> <20240304081348.197341-2-21cnbao@gmail.com> <01c61b90-df90-4819-978b-414bb717ef64@arm.com> In-Reply-To: <01c61b90-df90-4819-978b-414bb717ef64@arm.com> From: Barry Song <21cnbao@gmail.com> Date: Thu, 21 Mar 2024 21:42:38 +1300 Message-ID: Subject: Re: [RFC PATCH v3 1/5] arm64: mm: swap: support THP_SWAP on hardware with MTE To: Ryan Roberts Cc: akpm@linux-foundation.org, linux-mm@kvack.org, chengming.zhou@linux.dev, chrisl@kernel.org, david@redhat.com, hannes@cmpxchg.org, kasong@tencent.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, mhocko@suse.com, nphamcs@gmail.com, shy828301@gmail.com, steven.price@arm.com, surenb@google.com, wangkefeng.wang@huawei.com, willy@infradead.org, xiang@kernel.org, ying.huang@intel.com, yosryahmed@google.com, yuzhao@google.com, Barry Song , Catalin Marinas , Will Deacon , Mark Rutland , Kemeng Shi , Anshuman Khandual , Peter Collingbourne , Peter Xu , Lorenzo Stoakes , "Mike Rapoport (IBM)" , Hugh Dickins , "Aneesh Kumar K.V" , Rick Edgecombe Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 7DA78A001F X-Stat-Signature: hcirx5zdts4bcbp9anpi8bjubr3zmq1a X-HE-Tag: 1711010570-987350 X-HE-Meta: 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 89DAY3QS CWG70sTUas9P0evh5Th3uvEws5Wz9WTYvqiO/9JwHuzwyg3nBeJo8nd5Dzmu0Gy1JHvEe8jOQRhjQ+iAdd2K6oCvy9Q== 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: Hi Ryan, Sorry for the late reply. On Tue, Mar 12, 2024 at 5:56=E2=80=AFAM Ryan Roberts = wrote: > > On 04/03/2024 08:13, Barry Song wrote: > > From: Barry Song > > > > Commit d0637c505f8a1 ("arm64: enable THP_SWAP for arm64") brings up > > THP_SWAP on ARM64, but it doesn't enable THP_SWP on hardware with > > MTE as the MTE code works with the assumption tags save/restore is > > always handling a folio with only one page. > > > > The limitation should be removed as more and more ARM64 SoCs have > > this feature. Co-existence of MTE and THP_SWAP becomes more and > > more important. > > > > This patch makes MTE tags saving support large folios, then we don't > > need to split large folios into base pages for swapping out on ARM64 > > SoCs with MTE any more. > > > > arch_prepare_to_swap() should take folio rather than page as parameter > > because we support THP swap-out as a whole. It saves tags for all > > pages in a large folio. > > > > As now we are restoring tags based-on folio, in arch_swap_restore(), > > we may increase some extra loops and early-exitings while refaulting > > a large folio which is still in swapcache in do_swap_page(). In case > > a large folio has nr pages, do_swap_page() will only set the PTE of > > the particular page which is causing the page fault. > > Thus do_swap_page() runs nr times, and each time, arch_swap_restore() > > will loop nr times for those subpages in the folio. So right now the > > algorithmic complexity becomes O(nr^2). > > > > Once we support mapping large folios in do_swap_page(), extra loops > > and early-exitings will decrease while not being completely removed > > as a large folio might get partially tagged in corner cases such as, > > 1. a large folio in swapcache can be partially unmapped, thus, MTE > > tags for the unmapped pages will be invalidated; > > 2. users might use mprotect() to set MTEs on a part of a large folio. > > > > arch_thp_swp_supported() is dropped since ARM64 MTE was the only one > > who needed it. > > > > Cc: Catalin Marinas > > Cc: Will Deacon > > Cc: Ryan Roberts > > Cc: Mark Rutland > > Cc: David Hildenbrand > > Cc: Kemeng Shi > > Cc: "Matthew Wilcox (Oracle)" > > Cc: Anshuman Khandual > > Cc: Peter Collingbourne > > Cc: Steven Price > > Cc: Yosry Ahmed > > Cc: Peter Xu > > Cc: Lorenzo Stoakes > > Cc: "Mike Rapoport (IBM)" > > Cc: Hugh Dickins > > CC: "Aneesh Kumar K.V" > > Cc: Rick Edgecombe > > Signed-off-by: Barry Song > > Reviewed-by: Steven Price > > Acked-by: Chris Li > > --- > > arch/arm64/include/asm/pgtable.h | 19 ++------------ > > arch/arm64/mm/mteswap.c | 43 ++++++++++++++++++++++++++++++++ > > include/linux/huge_mm.h | 12 --------- > > include/linux/pgtable.h | 2 +- > > mm/page_io.c | 2 +- > > mm/swap_slots.c | 2 +- > > 6 files changed, 48 insertions(+), 32 deletions(-) > > > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/= pgtable.h > > index 401087e8a43d..7a54750770b8 100644 > > --- a/arch/arm64/include/asm/pgtable.h > > +++ b/arch/arm64/include/asm/pgtable.h > > @@ -45,12 +45,6 @@ > > __flush_tlb_range(vma, addr, end, PUD_SIZE, false, 1) > > #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > > > > -static inline bool arch_thp_swp_supported(void) > > -{ > > - return !system_supports_mte(); > > -} > > -#define arch_thp_swp_supported arch_thp_swp_supported > > - > > /* > > * Outside of a few very special situations (e.g. hibernation), we alw= ays > > * use broadcast TLB invalidation instructions, therefore a spurious p= age > > @@ -1095,12 +1089,7 @@ static inline pmd_t pmdp_establish(struct vm_are= a_struct *vma, > > #ifdef CONFIG_ARM64_MTE > > > > #define __HAVE_ARCH_PREPARE_TO_SWAP > > -static inline int arch_prepare_to_swap(struct page *page) > > -{ > > - if (system_supports_mte()) > > - return mte_save_tags(page); > > - return 0; > > -} > > +extern int arch_prepare_to_swap(struct folio *folio); > > > > #define __HAVE_ARCH_SWAP_INVALIDATE > > static inline void arch_swap_invalidate_page(int type, pgoff_t offset) > > @@ -1116,11 +1105,7 @@ static inline void arch_swap_invalidate_area(int= type) > > } > > > > #define __HAVE_ARCH_SWAP_RESTORE > > -static inline void arch_swap_restore(swp_entry_t entry, struct folio *= folio) > > -{ > > - if (system_supports_mte()) > > - mte_restore_tags(entry, &folio->page); > > -} > > +extern void arch_swap_restore(swp_entry_t entry, struct folio *folio); > > > > #endif /* CONFIG_ARM64_MTE */ > > > > diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c > > index a31833e3ddc5..295836fef620 100644 > > --- a/arch/arm64/mm/mteswap.c > > +++ b/arch/arm64/mm/mteswap.c > > @@ -68,6 +68,13 @@ void mte_invalidate_tags(int type, pgoff_t offset) > > mte_free_tag_storage(tags); > > } > > > > +static inline void __mte_invalidate_tags(struct page *page) > > +{ > > + swp_entry_t entry =3D page_swap_entry(page); > > + > > + mte_invalidate_tags(swp_type(entry), swp_offset(entry)); > > +} > > + > > void mte_invalidate_tags_area(int type) > > { > > swp_entry_t entry =3D swp_entry(type, 0); > > @@ -83,3 +90,39 @@ void mte_invalidate_tags_area(int type) > > } > > xa_unlock(&mte_pages); > > } > > + > > +int arch_prepare_to_swap(struct folio *folio) > > +{ > > + long i, nr; > > + int err; > > + > > + if (!system_supports_mte()) > > + return 0; > > + > > + nr =3D folio_nr_pages(folio); > > + > > + for (i =3D 0; i < nr; i++) { > > + err =3D mte_save_tags(folio_page(folio, i)); > > + if (err) > > + goto out; > > + } > > + return 0; > > + > > +out: > > + while (i--) > > + __mte_invalidate_tags(folio_page(folio, i)); > > + return err; > > +} > > + > > +void arch_swap_restore(swp_entry_t entry, struct folio *folio) > > I'm still not a fan of the fact that entry could be anywhere within folio= . > > > +{ > > + if (system_supports_mte()) { > > nit: if you do: > > if (!system_supports_mte()) > return; Acked > > It will be consistent with arch_prepare_to_swap() and reduce the indentat= ion of > the main body. > > > + long i, nr =3D folio_nr_pages(folio); > > + > > + entry.val -=3D swp_offset(entry) & (nr - 1); > > This assumes that folios are always stored in swap with natural alignment= . Is > that definitely a safe assumption? My swap-out series is currently ensuri= ng that > folios are swapped-out naturally aligned, but that is an implementation d= etail. > I concur that this is an implementation detail. However, we should be bold enough to state that swap slots will be contiguous, considering we are currently utilizing folio->swap instead of subpage->swap ? > Your cover note for swap-in says that you could technically swap in a lar= ge > folio without it having been swapped-out large. If you chose to do that i= n > future, this would break, right? I don't think it's good to couple the sw= ap Right. technically I agree. Given that we still have many tasks involving e= ven swapping in contiguous swap slots, it's unlikely that swapping in large fol= ios for non-contiguous entries will occur in the foreseeable future :-) > storage layout to the folio order that you want to swap into. Perhaps tha= t's an > argument for passing each *page* to this function with its exact, corresp= onding > swap entry? I recall Matthew Wilcox strongly objected to using "page" as the parameter, so I've discarded that approach. Alternatively, it appears I can consistently pass folio->swap to this function and ensure the function always retrieves the first entry? > > > + for (i =3D 0; i < nr; i++) { > > + mte_restore_tags(entry, folio_page(folio, i)); > > + entry.val++; > > + } > > + } > > +} > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > > index de0c89105076..e04b93c43965 100644 > > --- a/include/linux/huge_mm.h > > +++ b/include/linux/huge_mm.h > > @@ -535,16 +535,4 @@ static inline int split_folio_to_order(struct foli= o *folio, int new_order) > > #define split_folio_to_list(f, l) split_folio_to_list_to_order(f, l, 0= ) > > #define split_folio(f) split_folio_to_order(f, 0) > > > > -/* > > - * archs that select ARCH_WANTS_THP_SWAP but don't support THP_SWP due= to > > - * limitations in the implementation like arm64 MTE can override this = to > > - * false > > - */ > > -#ifndef arch_thp_swp_supported > > -static inline bool arch_thp_swp_supported(void) > > -{ > > - return true; > > -} > > -#endif > > - > > #endif /* _LINUX_HUGE_MM_H */ > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > > index e1b22903f709..bfcfe3386934 100644 > > --- a/include/linux/pgtable.h > > +++ b/include/linux/pgtable.h > > @@ -1106,7 +1106,7 @@ static inline int arch_unmap_one(struct mm_struct= *mm, > > * prototypes must be defined in the arch-specific asm/pgtable.h file. > > */ > > #ifndef __HAVE_ARCH_PREPARE_TO_SWAP > > -static inline int arch_prepare_to_swap(struct page *page) > > +static inline int arch_prepare_to_swap(struct folio *folio) > > { > > return 0; > > } > > diff --git a/mm/page_io.c b/mm/page_io.c > > index ae2b49055e43..a9a7c236aecc 100644 > > --- a/mm/page_io.c > > +++ b/mm/page_io.c > > @@ -189,7 +189,7 @@ int swap_writepage(struct page *page, struct writeb= ack_control *wbc) > > * Arch code may have to preserve more data than just the page > > * contents, e.g. memory tags. > > */ > > - ret =3D arch_prepare_to_swap(&folio->page); > > + ret =3D arch_prepare_to_swap(folio); > > if (ret) { > > folio_mark_dirty(folio); > > folio_unlock(folio); > > diff --git a/mm/swap_slots.c b/mm/swap_slots.c > > index 90973ce7881d..53abeaf1371d 100644 > > --- a/mm/swap_slots.c > > +++ b/mm/swap_slots.c > > @@ -310,7 +310,7 @@ swp_entry_t folio_alloc_swap(struct folio *folio) > > entry.val =3D 0; > > > > if (folio_test_large(folio)) { > > - if (IS_ENABLED(CONFIG_THP_SWAP) && arch_thp_swp_supported= ()) > > + if (IS_ENABLED(CONFIG_THP_SWAP)) > > get_swap_pages(1, &entry, folio_nr_pages(folio)); > > goto out; > > } > Thanks Barry