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Shutemov" , Jerome Glisse , peterx@redhat.com, Liam Howlett , Mike Rapoport Subject: [PATCH v3 5/5] mm: Add ZAP_FLAG_SKIP_SWAP and zap_flags Date: Wed, 8 Sep 2021 12:36:28 -0400 Message-Id: <20210908163628.215052-1-peterx@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210908163516.214441-1-peterx@redhat.com> References: <20210908163516.214441-1-peterx@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="US-ASCII" Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=gIdAQ6AN; spf=none (imf27.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: q4x1nrz6fbind3dbctqqxjcgmjynahgc X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 1633D700009B X-HE-Tag: 1631118992-671499 Content-Transfer-Encoding: quoted-printable 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: Firstly, the comment in zap_pte_range() is misleading because it checks a= gainst details rather than check_mappings, so it's against what the code did. Meanwhile, there's no explicit reason why passing in the details pointer = should mean to skip all swap entries. New user of zap_details could very possib= ly miss this fact if they don't read deep until zap_pte_range() because ther= e's no comment at zap_details talking about it at all, so swap entries could be erroneously skipped without being noticed. This partly reverts 3e8715fdc03e ("mm: drop zap_details::check_swap_entri= es"), but introduce ZAP_FLAG_SKIP_SWAP flag, which means the opposite of previo= us "details" parameter: the caller should explicitly set this to skip swap entries, otherwise swap entries will always be considered (which should s= till be the major case here). We may want to look into when exactly we need ZAP_FLAG_SKIP_SWAP and we s= hould have it in a synchronous manner, e.g., currently even if ZAP_FLAG_SKIP_SW= AP is set we'll still look into swap pmds no matter what. But that should be a separate effort of this patch. The flag introduced in this patch will be a preparation for more bits def= ined in the future, e.g., for a new bit in flag to show whether to persist the upcoming uffd-wp bit in pgtable entries. Cc: Kirill A. Shutemov Cc: Hugh Dickins Signed-off-by: Peter Xu --- include/linux/mm.h | 16 ++++++++++++++++ mm/memory.c | 6 +++--- 2 files changed, 19 insertions(+), 3 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index ed44f31615d9..beb784ce35b9 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1717,12 +1717,18 @@ static inline bool can_do_mlock(void) { return fa= lse; } extern int user_shm_lock(size_t, struct ucounts *); extern void user_shm_unlock(size_t, struct ucounts *); =20 +typedef unsigned int __bitwise zap_flags_t; + +/* Whether to skip zapping swap entries */ +#define ZAP_FLAG_SKIP_SWAP ((__force zap_flags_t) BIT(0)) + /* * Parameter block passed down to zap_pte_range in exceptional cases. */ struct zap_details { struct address_space *zap_mapping; /* Check page->mapping if set */ struct page *single_page; /* Locked page to be unmapped */ + zap_flags_t zap_flags; /* Extra flags for zapping */ }; =20 /* @@ -1739,6 +1745,16 @@ zap_skip_check_mapping(struct zap_details *details= , struct page *page) (details->zap_mapping !=3D page_rmapping(page)); } =20 +/* Return true if skip swap entries, false otherwise */ +static inline bool +zap_skip_swap(struct zap_details *details) +{ + if (!details) + return false; + + return details->zap_flags & ZAP_FLAG_SKIP_SWAP; +} + struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long ad= dr, pte_t pte); struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned lon= g addr, diff --git a/mm/memory.c b/mm/memory.c index e5ee8399d270..26e37bef1888 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1379,8 +1379,7 @@ static unsigned long zap_pte_range(struct mmu_gathe= r *tlb, continue; } =20 - /* If details->check_mapping, we leave swap entries. */ - if (unlikely(details)) + if (unlikely(zap_skip_swap(details))) continue; =20 if (!non_swap_entry(entry)) @@ -3353,6 +3352,7 @@ void unmap_mapping_page(struct page *page) =20 details.zap_mapping =3D mapping; details.single_page =3D page; + details.zap_flags =3D ZAP_FLAG_SKIP_SWAP; =20 i_mmap_lock_write(mapping); if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))) @@ -3377,7 +3377,7 @@ void unmap_mapping_pages(struct address_space *mapp= ing, pgoff_t start, pgoff_t nr, bool even_cows) { pgoff_t first_index =3D start, last_index =3D start + nr - 1; - struct zap_details details =3D { }; + struct zap_details details =3D { .zap_flags =3D ZAP_FLAG_SKIP_SWAP }; =20 details.zap_mapping =3D even_cows ? NULL : mapping; if (last_index < first_index) --=20 2.31.1