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Tue, 07 Nov 2023 10:05:23 -0800 (PST) MIME-Version: 1.0 References: <2fe5ce7e-9c5c-4df4-b4fc-9fd3d9b2dccb@arm.com> <20231104093423.170054-1-v-songbaohua@oppo.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Wed, 8 Nov 2023 02:05:10 +0800 Message-ID: Subject: Re: [PATCH v3 4/4] mm: swap: Swap-out small-sized THP without splitting To: Ryan Roberts Cc: steven.price@arm.com, akpm@linux-foundation.org, david@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, shy828301@gmail.com, wangkefeng.wang@huawei.com, willy@infradead.org, xiang@kernel.org, ying.huang@intel.com, yuzhao@google.com, Barry Song , nd@arm.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 66E9810001E X-Stat-Signature: p36w7tj13yznmh35apdw4jndx35je634 X-HE-Tag: 1699380324-622183 X-HE-Meta: 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 rs3rM3NZ 5Atd216M7LqDcdN42TWnQH84yZ9Q2j1K1dTPkOTACsRmXIJMV3zVqld/VI3jXnw1c3Ev4kXSHAVMf0UJ0tTkkpWP7tWQTu2OdoECR+g0wvl1CFuoK8XmqY679Li64+rPAw2RoQmO4SKiNBNj+3PpLg8kVYiArg4BDQDMQBHrhqWqnkgp8SuWKrBzJM127ekgfg6/XytT7RbDnGvmaFf1SGAMTGC1YUe7oZS5/00PUXKv3Dg6Xg2XdR0cc5w+oKdWzPi4+e6ABTeuXpQ6puFuNaQ5QlW0AxD0KlMF2qPWZUoYJdqic0D3BnJhtMDThz9lbGQTyiDtLZ6JTd+EdWRvKBzO8Y6RSlUXhTqLLp/DquZ+b/tmOacZWs7u3tpr5CBh7g7C4Bwjz43St4Qmnankgi4K/Phu3B1I+1HZjNyDb1zz0le/CKZjvWsiT/avzoKh9Fcq5ae/4vwn2hNWNxO7pK/bBUA== 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 Tue, Nov 7, 2023 at 8:46=E2=80=AFPM Ryan Roberts = wrote: > > On 04/11/2023 09:34, Barry Song wrote: > >> Yes that's right. mte_save_tags() needs to allocate memory so can fail > >> and if failing then arch_prepare_to_swap() would need to put things ba= ck > >> how they were with calls to mte_invalidate_tags() (although I think > >> you'd actually want to refactor to create a function which takes a > >> struct page *). > >> > >> Steve > > > > Thanks, Steve. combining all comments from You and Ryan, I made a v2. > > One tricky thing is that we are restoring one page rather than folio > > in arch_restore_swap() as we are only swapping in one page at this > > stage. > > > > [RFC v2 PATCH] arm64: mm: swap: save and restore mte tags for large fol= ios > > > > This patch makes MTE tags saving and restoring support large folios, > > then we don't need to split them into base pages for swapping on > > ARM64 SoCs with MTE. > > > > This patch moves arch_prepare_to_swap() to take folio rather than > > page, as we support THP swap-out as a whole. And this patch also > > drops arch_thp_swp_supported() as ARM64 MTE is the only one who > > needs it. > > > > Signed-off-by: Barry Song > > --- > > arch/arm64/include/asm/pgtable.h | 21 +++------------ > > arch/arm64/mm/mteswap.c | 44 ++++++++++++++++++++++++++++++++ > > include/linux/huge_mm.h | 12 --------- > > include/linux/pgtable.h | 2 +- > > mm/page_io.c | 2 +- > > mm/swap_slots.c | 2 +- > > 6 files changed, 51 insertions(+), 32 deletions(-) > > > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/= pgtable.h > > index b19a8aee684c..d8f523dc41e7 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 > > @@ -1036,12 +1030,8 @@ 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; > > -} > > +#define arch_prepare_to_swap arch_prepare_to_swap > > +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) > > @@ -1057,11 +1047,8 @@ 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); > > -} > > +#define arch_swap_restore arch_swap_restore > > +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..14a479e4ea8e 100644 > > --- a/arch/arm64/mm/mteswap.c > > +++ b/arch/arm64/mm/mteswap.c > > @@ -68,6 +68,12 @@ 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 +89,41 @@ void mte_invalidate_tags_area(int type) > > } > > xa_unlock(&mte_pages); > > } > > + > > +int arch_prepare_to_swap(struct folio *folio) > > +{ > > + int err; > > + long i; > > + > > + if (system_supports_mte()) { > > + long nr =3D folio_nr_pages(folio); > > nit: there should be a clear line between variable declarations and logic= . right. > > > + 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) > > If i is initially > 0, this will fail to invalidate page 0. If i is initi= ally 0 > then it will wrap and run ~forever. I think you meant `while (i--)`? nop. if i=3D0 and we goto out, that means the page0 has failed to save tags= , there is nothing to revert. if i=3D3 and we goto out, that means 0,1,2 have saved, we restore 0,1,2 and we don't restore 3. > > > + __mte_invalidate_tags(folio_page(folio, i)); > > + return err; > > +} > > + > > +void arch_swap_restore(swp_entry_t entry, struct folio *folio) > > +{ > > + if (system_supports_mte()) { > > + /* > > + * We don't support large folios swap in as whole yet, bu= t > > + * we can hit a large folio which is still in swapcache > > + * after those related processes' PTEs have been unmapped > > + * but before the swapcache folio is dropped, in this ca= se, > > + * we need to find the exact page which "entry" is mappin= g > > + * to. If we are not hitting swapcache, this folio won't = be > > + * large > > + */ > > So the currently defined API allows a large folio to be passed but the ca= ller is > supposed to find the single correct page using the swap entry? That feels= quite > nasty to me. And that's not what the old version of the function was doin= g; it > always assumed that the folio was small and passed the first page (which = also > doesn't feel 'nice'). If the old version was wrong, I suggest a separate = commit > to fix that. If the old version is correct, then I guess this version is = wrong. the original version(mainline) is wrong but it works as once we find the So= Cs support MTE, we will split large folios into small pages. so only small pag= es will be added into swapcache successfully. but now we want to swap out large folios even on SoCs with MTE as a whole, we don't split, so this breaks the assumption do_swap_page() will always ge= t small pages. > > Thanks, > Ryan > > > + struct page *page =3D folio_file_page(folio, swp_offset(e= ntry)); > > + mte_restore_tags(entry, page); > > + } > > +} > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > > index fa0350b0812a..f83fb8d5241e 100644 > > --- a/include/linux/huge_mm.h > > +++ b/include/linux/huge_mm.h > > @@ -400,16 +400,4 @@ static inline int split_folio(struct folio *folio) > > return split_folio_to_list(folio, NULL); > > } > > > > -/* > > - * 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 af7639c3b0a3..33ab4ddd91dd 100644 > > --- a/include/linux/pgtable.h > > +++ b/include/linux/pgtable.h > > @@ -897,7 +897,7 @@ 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 cb559ae324c6..0fd832474c1d 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 0bec1f705f8e..2325adbb1f19 100644 > > --- a/mm/swap_slots.c > > +++ b/mm/swap_slots.c > > @@ -307,7 +307,7 @@ 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