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X-CSE-ConnectionGUID: vxUxuyRoQjegm7piwakrSw== X-CSE-MsgGUID: u/mbdj6ZS+WxC1nXI3glCQ== X-IronPort-AV: E=McAfee;i="6700,10204,11149"; a="19971066" X-IronPort-AV: E=Sophos;i="6.09,251,1716274800"; d="scan'208";a="19971066" Received: from orviesa007.jf.intel.com ([10.64.159.147]) by fmvoesa113.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 Jul 2024 01:28:55 -0700 X-CSE-ConnectionGUID: RcqgeXpLTE+YXDZRGWN51Q== X-CSE-MsgGUID: JKw1WgDKSbOQ29QjKI9oLg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.09,251,1716274800"; d="scan'208";a="55209710" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by orviesa007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 Jul 2024 01:28:49 -0700 From: "Huang, Ying" To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, hannes@cmpxchg.org, hughd@google.com, kaleshsingh@google.com, kasong@tencent.com, linux-kernel@vger.kernel.org, mhocko@suse.com, minchan@kernel.org, nphamcs@gmail.com, ryan.roberts@arm.com, senozhatsky@chromium.org, shakeel.butt@linux.dev, shy828301@gmail.com, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, xiang@kernel.org, yosryahmed@google.com Subject: Re: [PATCH 1/1] mm: swap: add nr argument in swapcache_prepare and swapcache_clear to support large folios In-Reply-To: (Barry Song's message of "Wed, 31 Jul 2024 16:20:27 +0800") References: <20240730071339.107447-1-21cnbao@gmail.com> <20240730071339.107447-2-21cnbao@gmail.com> <874j86oubf.fsf@yhuang6-desk2.ccr.corp.intel.com> Date: Wed, 31 Jul 2024 16:25:16 +0800 Message-ID: <87zfpynf2r.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Barry Song <21cnbao@gmail.com> writes: > On Wed, Jul 31, 2024 at 4:14=E2=80=AFPM Huang, Ying wrote: >> >> Hi, Barry, >> >> Barry Song <21cnbao@gmail.com> writes: >> >> > From: Barry Song >> > >> > Right now, swapcache_prepare() and swapcache_clear() supports one entry >> > only, to support large folios, we need to handle multiple swap entries. >> > >> > To optimize stack usage, we iterate twice in __swap_duplicate(): the >> > first time to verify that all entries are valid, and the second time >> > to apply the modifications to the entries. >> > >> > Currently, we're using nr=3D1 for the existing users. >> > >> > Reviewed-by: Baolin Wang >> > Signed-off-by: Barry Song >> > --- >> > include/linux/swap.h | 4 +- >> > mm/memory.c | 6 +-- >> > mm/swap.h | 5 ++- >> > mm/swap_state.c | 2 +- >> > mm/swapfile.c | 101 +++++++++++++++++++++++++------------------ >> > 5 files changed, 68 insertions(+), 50 deletions(-) >> > >> > diff --git a/include/linux/swap.h b/include/linux/swap.h >> > index ba7ea95d1c57..5b920fa2315b 100644 >> > --- a/include/linux/swap.h >> > +++ b/include/linux/swap.h >> > @@ -480,7 +480,7 @@ extern int get_swap_pages(int n, swp_entry_t swp_e= ntries[], int order); >> > extern int add_swap_count_continuation(swp_entry_t, gfp_t); >> > extern void swap_shmem_alloc(swp_entry_t); >> > extern int swap_duplicate(swp_entry_t); >> > -extern int swapcache_prepare(swp_entry_t); >> > +extern int swapcache_prepare(swp_entry_t entry, int nr); >> > extern void swap_free_nr(swp_entry_t entry, int nr_pages); >> > extern void swapcache_free_entries(swp_entry_t *entries, int n); >> > extern void free_swap_and_cache_nr(swp_entry_t entry, int nr); >> > @@ -554,7 +554,7 @@ static inline int swap_duplicate(swp_entry_t swp) >> > return 0; >> > } >> > >> > -static inline int swapcache_prepare(swp_entry_t swp) >> > +static inline int swapcache_prepare(swp_entry_t swp, int nr) >> > { >> > return 0; >> > } >> > diff --git a/mm/memory.c b/mm/memory.c >> > index 833d2cad6eb2..b8675617a5e3 100644 >> > --- a/mm/memory.c >> > +++ b/mm/memory.c >> > @@ -4081,7 +4081,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >> > * reusing the same entry. It's undetectable as >> > * pte_same() returns true due to entry reuse. >> > */ >> > - if (swapcache_prepare(entry)) { >> > + if (swapcache_prepare(entry, 1)) { >> > /* Relax a bit to prevent rapid repeated= page faults */ >> > schedule_timeout_uninterruptible(1); >> > goto out; >> > @@ -4387,7 +4387,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >> > out: >> > /* Clear the swap cache pin for direct swapin after PTL unlock */ >> > if (need_clear_cache) >> > - swapcache_clear(si, entry); >> > + swapcache_clear(si, entry, 1); >> > if (si) >> > put_swap_device(si); >> > return ret; >> > @@ -4403,7 +4403,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >> > folio_put(swapcache); >> > } >> > if (need_clear_cache) >> > - swapcache_clear(si, entry); >> > + swapcache_clear(si, entry, 1); >> > if (si) >> > put_swap_device(si); >> > return ret; >> > diff --git a/mm/swap.h b/mm/swap.h >> > index baa1fa946b34..7c6330561d84 100644 >> > --- a/mm/swap.h >> > +++ b/mm/swap.h >> > @@ -59,7 +59,7 @@ void __delete_from_swap_cache(struct folio *folio, >> > void delete_from_swap_cache(struct folio *folio); >> > void clear_shadow_from_swap_cache(int type, unsigned long begin, >> > unsigned long end); >> > -void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry); >> > +void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, = int nr); >> > struct folio *swap_cache_get_folio(swp_entry_t entry, >> > struct vm_area_struct *vma, unsigned long addr); >> > struct folio *filemap_get_incore_folio(struct address_space *mapping, >> > @@ -120,7 +120,7 @@ static inline int swap_writepage(struct page *p, s= truct writeback_control *wbc) >> > return 0; >> > } >> > >> > -static inline void swapcache_clear(struct swap_info_struct *si, swp_e= ntry_t entry) >> > +static inline void swapcache_clear(struct swap_info_struct *si, swp_e= ntry_t entry, int nr) >> > { >> > } >> > >> > @@ -172,4 +172,5 @@ static inline unsigned int folio_swap_flags(struct= folio *folio) >> > return 0; >> > } >> > #endif /* CONFIG_SWAP */ >> > + >> >> NITPICK: Is it necessary to add a blank line here? But I don't think a >> new version is necessary if this is the only change needed. > > No need to add a blank line; it was probably a mistake I made in Vim. > >> >> > #endif /* _MM_SWAP_H */ >> > diff --git a/mm/swap_state.c b/mm/swap_state.c >> > index a1726e49a5eb..b06f2a054f5a 100644 >> > --- a/mm/swap_state.c >> > +++ b/mm/swap_state.c >> > @@ -477,7 +477,7 @@ struct folio *__read_swap_cache_async(swp_entry_t = entry, gfp_t gfp_mask, >> > /* >> > * Swap entry may have been freed since our caller obser= ved it. >> > */ >> > - err =3D swapcache_prepare(entry); >> > + err =3D swapcache_prepare(entry, 1); >> > if (!err) >> > break; >> > >> > diff --git a/mm/swapfile.c b/mm/swapfile.c >> > index 5f73a8553371..757d38a86f56 100644 >> > --- a/mm/swapfile.c >> > +++ b/mm/swapfile.c >> > @@ -3363,7 +3363,7 @@ void si_swapinfo(struct sysinfo *val) >> > } >> > >> > /* >> > - * Verify that a swap entry is valid and increment its swap map count. >> > + * Verify that nr swap entries are valid and increment their swap map= counts. >> > * >> > * Returns error code in following case. >> > * - success -> 0 >> > @@ -3373,60 +3373,77 @@ void si_swapinfo(struct sysinfo *val) >> > * - swap-cache reference is requested but the entry is not used. -> = ENOENT >> > * - swap-mapped reference requested but needs continued swap count. = -> ENOMEM >> > */ >> > -static int __swap_duplicate(swp_entry_t entry, unsigned char usage) >> > +static int __swap_duplicate(swp_entry_t entry, unsigned char usage, i= nt nr) >> > { >> > struct swap_info_struct *p; >> > struct swap_cluster_info *ci; >> > unsigned long offset; >> > unsigned char count; >> > unsigned char has_cache; >> > - int err; >> > + int err, i; >> > >> > p =3D swp_swap_info(entry); >> > >> > offset =3D swp_offset(entry); >> > + VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER); >> > ci =3D lock_cluster_or_swap_info(p, offset); >> > >> > - count =3D p->swap_map[offset]; >> > + err =3D 0; >> > + for (i =3D 0; i < nr; i++) { >> > + count =3D p->swap_map[offset + i]; >> > >> > - /* >> > - * swapin_readahead() doesn't check if a swap entry is valid, so= the >> > - * swap entry could be SWAP_MAP_BAD. Check here with lock held. >> > - */ >> > - if (unlikely(swap_count(count) =3D=3D SWAP_MAP_BAD)) { >> > - err =3D -ENOENT; >> > - goto unlock_out; >> > - } >> > + /* >> > + * swapin_readahead() doesn't check if a swap entry is v= alid, so the >> > + * swap entry could be SWAP_MAP_BAD. Check here with loc= k held. >> > + */ >> > + if (unlikely(swap_count(count) =3D=3D SWAP_MAP_BAD)) { >> > + err =3D -ENOENT; >> > + goto unlock_out; >> > + } >> > >> > - has_cache =3D count & SWAP_HAS_CACHE; >> > - count &=3D ~SWAP_HAS_CACHE; >> > - err =3D 0; >> > + has_cache =3D count & SWAP_HAS_CACHE; >> > + count &=3D ~SWAP_HAS_CACHE; >> > >> > - if (usage =3D=3D SWAP_HAS_CACHE) { >> > + if (usage =3D=3D SWAP_HAS_CACHE) { >> > + /* set SWAP_HAS_CACHE if there is no cache and e= ntry is used */ >> > + if (!has_cache && count) >> > + continue; >> > + else if (has_cache) /* someone else = added cache */ >> > + err =3D -EEXIST; >> > + else /* no users rema= ining */ >> > + err =3D -ENOENT; >> > >> > - /* set SWAP_HAS_CACHE if there is no cache and entry is = used */ >> > - if (!has_cache && count) >> > - has_cache =3D SWAP_HAS_CACHE; >> > - else if (has_cache) /* someone else added ca= che */ >> > - err =3D -EEXIST; >> > - else /* no users remaining */ >> > - err =3D -ENOENT; >> > + } else if (count || has_cache) { >> > >> > - } else if (count || has_cache) { >> > + if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX) >> > + continue; >> > + else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_M= AX) >> > + err =3D -EINVAL; >> > + else if (swap_count_continued(p, offset + i, cou= nt)) >> > + continue; >> >> IIUC, this will make the change to swap map directly instead of >> verification. If the verification failed for some entry later, the >> count will be wrong? Or I missed something? > > To avoid using a bitmap or a larger stack, we actually verify during > the first iteration. > This ensures that by the second iteration, we can safely commit the > modification. > > I actually put some words in the changelog :-) > > To optimize stack usage, we iterate twice in __swap_duplicate(): the > first time to verify that all entries are valid, and the second time > to apply the modifications to the entries. Yes, I have seen it and I think that it is a good strategy. But, IIUC, swap_count_continued() will change the higher bits of the swap_map instead of verifying. Or, my understanding is wrong? -- Best Regards, Huang, Ying >> >> > + else >> > + err =3D -ENOMEM; >> > + } else >> > + err =3D -ENOENT; /* unused swap= entry */ >> > >> > - if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX) >> > + if (err) >> > + goto unlock_out; >> > + } >> > + >> > + for (i =3D 0; i < nr; i++) { >> > + count =3D p->swap_map[offset + i]; >> > + has_cache =3D count & SWAP_HAS_CACHE; >> > + count &=3D ~SWAP_HAS_CACHE; >> > + >> > + if (usage =3D=3D SWAP_HAS_CACHE) >> > + has_cache =3D SWAP_HAS_CACHE; >> > + else if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX) >> > count +=3D usage; >> > - else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX) >> > - err =3D -EINVAL; >> > - else if (swap_count_continued(p, offset, count)) >> > - count =3D COUNT_CONTINUED; >> > else >> > - err =3D -ENOMEM; >> > - } else >> > - err =3D -ENOENT; /* unused swap entry */ >> > + count =3D COUNT_CONTINUED; >> > >> > - if (!err) >> > - WRITE_ONCE(p->swap_map[offset], count | has_cache); >> > + WRITE_ONCE(p->swap_map[offset + i], count | has_cache); >> > + } >> > >> > unlock_out: >> > unlock_cluster_or_swap_info(p, ci); >> > @@ -3439,7 +3456,7 @@ static int __swap_duplicate(swp_entry_t entry, u= nsigned char usage) >> > */ >> > void swap_shmem_alloc(swp_entry_t entry) >> > { >> > - __swap_duplicate(entry, SWAP_MAP_SHMEM); >> > + __swap_duplicate(entry, SWAP_MAP_SHMEM, 1); >> > } >> > >> > /* >> > @@ -3453,29 +3470,29 @@ int swap_duplicate(swp_entry_t entry) >> > { >> > int err =3D 0; >> > >> > - while (!err && __swap_duplicate(entry, 1) =3D=3D -ENOMEM) >> > + while (!err && __swap_duplicate(entry, 1, 1) =3D=3D -ENOMEM) >> > err =3D add_swap_count_continuation(entry, GFP_ATOMIC); >> > return err; >> > } >> > >> > /* >> > - * @entry: swap entry for which we allocate swap cache. >> > + * @entry: first swap entry from which we allocate nr swap cache. >> > * >> > - * Called when allocating swap cache for existing swap entry, >> > + * Called when allocating swap cache for existing swap entries, >> > * This can return error codes. Returns 0 at success. >> > * -EEXIST means there is a swap cache. >> > * Note: return code is different from swap_duplicate(). >> > */ >> > -int swapcache_prepare(swp_entry_t entry) >> > +int swapcache_prepare(swp_entry_t entry, int nr) >> > { >> > - return __swap_duplicate(entry, SWAP_HAS_CACHE); >> > + return __swap_duplicate(entry, SWAP_HAS_CACHE, nr); >> > } >> > >> > -void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry) >> > +void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, = int nr) >> > { >> > unsigned long offset =3D swp_offset(entry); >> > >> > - cluster_swap_free_nr(si, offset, 1, SWAP_HAS_CACHE); >> > + cluster_swap_free_nr(si, offset, nr, SWAP_HAS_CACHE); >> > } >> > >> > struct swap_info_struct *swp_swap_info(swp_entry_t entry) >> >> -- >> Best Regards, >> Huang, Ying > > Thanks > Barry