diff options
author | Hugh Dickins <hughd@google.com> | 2022-02-14 18:21:52 -0800 |
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committer | Matthew Wilcox (Oracle) <willy@infradead.org> | 2022-02-17 11:56:36 -0500 |
commit | b67bf49ce7aae72f63739abee6ac25f64bf20081 (patch) | |
tree | e94cfac0f8ad4e293bf4aa3d4370ab7a5cd473e7 /mm | |
parent | mm/munlock: delete page_mlock() and all its works (diff) | |
download | linux-b67bf49ce7aae72f63739abee6ac25f64bf20081.tar.gz linux-b67bf49ce7aae72f63739abee6ac25f64bf20081.tar.bz2 linux-b67bf49ce7aae72f63739abee6ac25f64bf20081.zip |
mm/munlock: delete FOLL_MLOCK and FOLL_POPULATE
If counting page mlocks, we must not double-count: follow_page_pte() can
tell if a page has already been Mlocked or not, but cannot tell if a pte
has already been counted or not: that will have to be done when the pte
is mapped in (which lru_cache_add_inactive_or_unevictable() already tracks
for new anon pages, but there's no such tracking yet for others).
Delete all the FOLL_MLOCK code - faulting in the missing pages will do
all that is necessary, without special mlock_vma_page() calls from here.
But then FOLL_POPULATE turns out to serve no purpose - it was there so
that its absence would tell faultin_page() not to faultin page when
setting up VM_LOCKONFAULT areas; but if there's no special work needed
here for mlock, then there's no work at all here for VM_LOCKONFAULT.
Have I got that right? I've not looked into the history, but see that
FOLL_POPULATE goes back before VM_LOCKONFAULT: did it serve a different
purpose before? Ah, yes, it was used to skip the old stack guard page.
And is it intentional that COW is not broken on existing pages when
setting up a VM_LOCKONFAULT area? I can see that being argued either
way, and have no reason to disagree with current behaviour.
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/gup.c | 43 | ||||
-rw-r--r-- | mm/huge_memory.c | 33 |
2 files changed, 8 insertions, 68 deletions
@@ -597,32 +597,6 @@ retry: */ mark_page_accessed(page); } - if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) { - /* Do not mlock pte-mapped THP */ - if (PageTransCompound(page)) - goto out; - - /* - * The preliminary mapping check is mainly to avoid the - * pointless overhead of lock_page on the ZERO_PAGE - * which might bounce very badly if there is contention. - * - * If the page is already locked, we don't need to - * handle it now - vmscan will handle it later if and - * when it attempts to reclaim the page. - */ - if (page->mapping && trylock_page(page)) { - lru_add_drain(); /* push cached pages to LRU */ - /* - * Because we lock page here, and migration is - * blocked by the pte's page reference, and we - * know the page is still mapped, we don't even - * need to check for file-cache page truncation. - */ - mlock_vma_page(page); - unlock_page(page); - } - } out: pte_unmap_unlock(ptep, ptl); return page; @@ -945,9 +919,6 @@ static int faultin_page(struct vm_area_struct *vma, unsigned int fault_flags = 0; vm_fault_t ret; - /* mlock all present pages, but do not fault in new pages */ - if ((*flags & (FOLL_POPULATE | FOLL_MLOCK)) == FOLL_MLOCK) - return -ENOENT; if (*flags & FOLL_NOFAULT) return -EFAULT; if (*flags & FOLL_WRITE) @@ -1198,8 +1169,6 @@ retry: case -ENOMEM: case -EHWPOISON: goto out; - case -ENOENT: - goto next_page; } BUG(); } else if (PTR_ERR(page) == -EEXIST) { @@ -1497,9 +1466,14 @@ long populate_vma_page_range(struct vm_area_struct *vma, VM_BUG_ON_VMA(end > vma->vm_end, vma); mmap_assert_locked(mm); - gup_flags = FOLL_TOUCH | FOLL_POPULATE | FOLL_MLOCK; + /* + * Rightly or wrongly, the VM_LOCKONFAULT case has never used + * faultin_page() to break COW, so it has no work to do here. + */ if (vma->vm_flags & VM_LOCKONFAULT) - gup_flags &= ~FOLL_POPULATE; + return nr_pages; + + gup_flags = FOLL_TOUCH; /* * We want to touch writable mappings with a write fault in order * to break COW, except for shared mappings because these don't COW @@ -1566,10 +1540,9 @@ long faultin_vma_page_range(struct vm_area_struct *vma, unsigned long start, * in the page table. * FOLL_HWPOISON: Return -EHWPOISON instead of -EFAULT when we hit * a poisoned page. - * FOLL_POPULATE: Always populate memory with VM_LOCKONFAULT. * !FOLL_FORCE: Require proper access permissions. */ - gup_flags = FOLL_TOUCH | FOLL_POPULATE | FOLL_MLOCK | FOLL_HWPOISON; + gup_flags = FOLL_TOUCH | FOLL_HWPOISON; if (write) gup_flags |= FOLL_WRITE; diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 406a3c28c026..9a34b85ebcf8 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1380,39 +1380,6 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, if (flags & FOLL_TOUCH) touch_pmd(vma, addr, pmd, flags); - if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) { - /* - * We don't mlock() pte-mapped THPs. This way we can avoid - * leaking mlocked pages into non-VM_LOCKED VMAs. - * - * For anon THP: - * - * In most cases the pmd is the only mapping of the page as we - * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for - * writable private mappings in populate_vma_page_range(). - * - * The only scenario when we have the page shared here is if we - * mlocking read-only mapping shared over fork(). We skip - * mlocking such pages. - * - * For file THP: - * - * We can expect PageDoubleMap() to be stable under page lock: - * for file pages we set it in page_add_file_rmap(), which - * requires page to be locked. - */ - - if (PageAnon(page) && compound_mapcount(page) != 1) - goto skip_mlock; - if (PageDoubleMap(page) || !page->mapping) - goto skip_mlock; - if (!trylock_page(page)) - goto skip_mlock; - if (page->mapping && !PageDoubleMap(page)) - mlock_vma_page(page); - unlock_page(page); - } -skip_mlock: page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT; VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page); |