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Fri, 22 Mar 2024 00:41:56 -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: From: Barry Song <21cnbao@gmail.com> Date: Fri, 22 Mar 2024 20:41:45 +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-Rspamd-Queue-Id: 1E1F1180013 X-Rspam-User: X-Stat-Signature: 6kbgse9u5xgowtg3afqw8hpaar59wyxo X-Rspamd-Server: rspam01 X-HE-Tag: 1711093317-660177 X-HE-Meta: U2FsdGVkX1+S579dWk6l4NUiT4leBbFxmjWuk+oMR+6/YH8IQ+k/szvs8m7c8XlSDLG2AZSAhMgxTfHWMpCxOycT2uNkvbXZ8OxE4quXy+nPED5yKeMV2xoM/njbydT2/bsAhNzJJ8iLxXjEXtAu1IGRyvpIqbt1/BN5g2M34tQFMnAxaKMDJUaVEaXosnMPf6SV9Y1QiCM61UOTic35JbZznEg7rv14bjp07iY16xUmtIp44PzDy3dR0nzajdFKViTBUsUFeDEHuoW4hcB4FFTUxqYY9sgOUk/TzcQqTYp27JC0TeFzBTnwQASSfGRFwrpajfcL27O4Irdk/5HEeD8jb/FEDiSNUbr2fD4U8xitXpKdx+MfKhIqVqJdNwY98LIeAJm7JpQCHEhOOYdl1hK2hERJUTmlELvjuwZSLwIbrNISjZrR9hM9jy+gskD7N/SYkACpM+xwDN2cIAAVIfsuFa2tAvGyRUe1cL+v1AawGIE6JR0HrCIsoXiy2XYytdg8Wa3STt4lu2UhPq5gE6641/eA1FVQMQ+Exg81QNuxbmkB5++ZY2ZrxZUrmZwzAKqYdhjBa1EgLwCXxB8LfXgSAzD8iCQCYuiImJEJRcWuf2K5fyw/YjVAkLlSCSHnnGzxpjbtSAhiPzoYRnjfhqfDzX7aZaqjcFX9NyDkVEFxgt70j/97lEPz623r2gUbtPsUFnLa6lHVS26zTWEL4jx5qGOdO5Cip2rQPxe3gCSm32tZNFPtkOxp5hBnh3qFQ4AqdKM5NbjNh5s8ARwDNiWw3Xs3lZbEBVlOnIKnygzFWfJGj5oyg1Pu2gUXz0Mx0Iv19LC6Xwhsx5zjB5qP0K/Qw+mXmjZsHe7Sqxn9PemvQoAAXzKWu5IOcvMCfWFn61n8OKH6iDKIN10Gv68Q4LeN5mnBumtnF47SKobJSBYBtu5haOPxJNClOhqS6NNe1UR7pGYfAB8aRs0+QVV dRbPILJN L4B7TF1OizuVUFWHtlpzpPberSrhBqzQL7OMgC2LbCiW2NteUOnTxijc/BZjOVaJJQHsmozOtkGKaO95h0wO24nFBbQ== 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 Fri, Mar 22, 2024 at 3:51=E2=80=AFPM Barry Song <21cnbao@gmail.com> wrot= e: > > On Thu, Mar 21, 2024 at 11:31=E2=80=AFPM Ryan Roberts wrote: > > > > On 21/03/2024 08:42, Barry Song wrote: > > > Hi Ryan, > > > Sorry for the late reply. > > > > No problem! > > > > > > > > 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 ARM6= 4 > > >>> SoCs with MTE any more. > > >>> > > >>> arch_prepare_to_swap() should take folio rather than page as parame= ter > > >>> 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 refaultin= g > > >>> a large folio which is still in swapcache in do_swap_page(). In cas= e > > >>> 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 th= e > > >>> 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 foli= o. > > >>> > > >>> arch_thp_swp_supported() is dropped since ARM64 MTE was the only on= e > > >>> who needed it. > > > > I think we should decouple this patch from your swap-in series. I suspe= ct this > > one could be ready and go in sooner than the swap-in series based on th= e current > > discussions :) > > > > >>> > > >>> 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= always > > >>> * use broadcast TLB invalidation instructions, therefore a spurio= us page > > >>> @@ -1095,12 +1089,7 @@ static inline pmd_t pmdp_establish(struct vm= _area_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 off= set) > > >>> @@ -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 fol= io *folio) > > >>> -{ > > >>> - if (system_supports_mte()) > > >>> - mte_restore_tags(entry, &folio->page); > > >>> -} > > >>> +extern void arch_swap_restore(swp_entry_t entry, struct folio *fol= io); > > >>> > > >>> #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 offse= t) > > >>> 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 ind= entation 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 alig= nment. Is > > >> that definitely a safe assumption? My swap-out series is currently e= nsuring that > > >> folios are swapped-out naturally aligned, but that is an implementat= ion detail. > > >> > > > > > > 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 ? > > > > Yes, I agree about contiguity. My objection is about assuming natural a= lignment > > though. It can still be contiguous while not naturally aligned in swap. > > Hi Ryan, > > While working on the new version of this patch, I've come to recognize > that, for the time being, it's > imperative to maintain a natural alignment. The following code > operates on the basis of this > assumption. > > /** > * folio_file_page - The page for a particular index. > * @folio: The folio which contains this index. > * @index: The index we want to look up. > * > * Sometimes after looking up a folio in the page cache, we need to > * obtain the specific page for an index (eg a page fault). > * > * Return: The page containing the file data for this index. > */ > static inline struct page *folio_file_page(struct folio *folio, pgoff_t i= ndex) > { > return folio_page(folio, index & (folio_nr_pages(folio) - 1)); > } > > > It's invoked everywhere, particularly within do_swap_page(). Nonetheless, > I remain confident that I can consistently pass the first entry to > arch_swap_restore(). After grappling for a couple of hours, I've realized that the only viable approach is as follows: shifting the task of obtaining the first entry from the callee to the callers( looks silly). This is necessary due to various scenarios like swap cache, non-swap cache, and KSM, each presenting different cases. Since there's no assurance of folio->swap being present, forcibly setting folio->swap could = pose risks (There might not even be any risk involved, but the associated task getting the first entry still cannot be overlooked by callers). diff --git a/mm/internal.h b/mm/internal.h index 7e486f2c502c..94d5b4b5a5da 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -76,6 +76,20 @@ static inline int folio_nr_pages_mapped(struct folio *fo= lio) return atomic_read(&folio->_nr_pages_mapped) & FOLIO_PAGES_MAPPED; } +/* + * Retrieve the first entry of a folio based on a provided entry within th= e + * folio. We cannot rely on folio->swap as there is no guarantee that it h= as + * been initialized. Used by arch_swap_restore() + */ +static inline swp_entry_t folio_swap(swp_entry_t entry, struct folio *foli= o) +{ + swp_entry_t swap =3D { + .val =3D entry.val & (folio_nr_pages(folio) - 1), + }; + + return swap; +} + static inline void *folio_raw_mapping(struct folio *folio) { unsigned long mapping =3D (unsigned long)folio->mapping; diff --git a/mm/memory.c b/mm/memory.c index f2bc6dd15eb8..b7cab8be8632 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4188,7 +4188,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) * when reading from swap. This metadata may be indexed by swap ent= ry * so this must be called before swap_free(). */ - arch_swap_restore(entry, folio); + arch_swap_restore(folio_swap(entry, folio), folio); /* * Remove the swap entry and conditionally try to free up the swapc= ache. diff --git a/mm/shmem.c b/mm/shmem.c index 0aad0d9a621b..82c9df4628f2 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1913,7 +1913,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, * Some architectures may have to restore extra metadata to the * folio after reading from swap. */ - arch_swap_restore(swap, folio); + arch_swap_restore(folio_swap(entry, folio), folio); if (shmem_should_replace_folio(folio, gfp)) { error =3D shmem_replace_folio(&folio, gfp, info, index); diff --git a/mm/swapfile.c b/mm/swapfile.c index 4919423cce76..5e6d2304a2a4 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1806,7 +1806,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, * when reading from swap. This metadata may be indexed by swap ent= ry * so this must be called before swap_free(). */ - arch_swap_restore(entry, folio); + arch_swap_restore(folio_swap(entry, folio), folio); dec_mm_counter(vma->vm_mm, MM_SWAPENTS); inc_mm_counter(vma->vm_mm, MM_ANONPAGES); Meanwhile, natural alignment is essential even during the execution of add_to_swap(), as failure to do so will trigger the VM_BUG_ON condition below. int add_to_swap_cache(struct folio *folio, swp_entry_t entry, gfp_t gfp, void **shadowp) { struct address_space *address_space =3D swap_address_space(entry); pgoff_t idx =3D swp_offset(entry); XA_STATE_ORDER(xas, &address_space->i_pages, idx, folio_order(folio= )); unsigned long i, nr =3D folio_nr_pages(folio); ... folio_set_swapcache(folio); folio->swap =3D entry; do { xas_lock_irq(&xas); xas_create_range(&xas); if (xas_error(&xas)) goto unlock; for (i =3D 0; i < nr; i++) { VM_BUG_ON_FOLIO(xas.xa_index !=3D idx + i, folio); if (shadowp) { old =3D xas_load(&xas); if (xa_is_value(old)) *shadowp =3D old; } xas_store(&xas, folio); xas_next(&xas); } } Based on the information provided, Ryan, would it be feasible to retain the= task of obtaining the first entry within the callee? Or, are you in favor of utilizing the new folio_swap() helper? > > > > > > > > >> Your cover note for swap-in says that you could technically swap in = a large > > >> folio without it having been swapped-out large. If you chose to do t= hat in > > >> future, this would break, right? I don't think it's good to couple t= he swap > > > > > > Right. technically I agree. Given that we still have many tasks invol= ving even > > > swapping in contiguous swap slots, it's unlikely that swapping in lar= ge folios > > > for non-contiguous entries will occur in the foreseeable future :-) > > > > > >> storage layout to the folio order that you want to swap into. Perhap= s that's an > > >> argument for passing each *page* to this function with its exact, co= rresponding > > >> 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? > > > > Yes, if we must pass a folio here, I'd prefer that entry always corresp= onds to > > the first entry for the folio. That will remove the need for this funct= ion to do > > the alignment above too. So win-win. > > > > > > > >> > > >>> + 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 = folio *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 t= his 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_st= ruct *mm, > > >>> * prototypes must be defined in the arch-specific asm/pgtable.h f= ile. > > >>> */ > > >>> #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 wr= iteback_control *wbc) > > >>> * Arch code may have to preserve more data than just the pag= e > > >>> * 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 *foli= o) > > >>> entry.val =3D 0; > > >>> > > >>> if (folio_test_large(folio)) { > > >>> - if (IS_ENABLED(CONFIG_THP_SWAP) && arch_thp_swp_suppo= rted()) > > >>> + if (IS_ENABLED(CONFIG_THP_SWAP)) > > >>> get_swap_pages(1, &entry, folio_nr_pages(foli= o)); > > >>> goto out; > > >>> } > > >> > > > > > > Thanks > > > Barry > >