Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752079AbdH3DQt (ORCPT ); Tue, 29 Aug 2017 23:16:49 -0400 Received: from mail-pg0-f67.google.com ([74.125.83.67]:36604 "EHLO mail-pg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751778AbdH3DQs (ORCPT ); Tue, 29 Aug 2017 23:16:48 -0400 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 10.3 \(3273\)) Subject: Re: [PATCH 02/13] mm/rmap: update to new mmu_notifier semantic From: Nadav Amit In-Reply-To: <20170830025910.GB2386@redhat.com> Date: Tue, 29 Aug 2017 20:16:44 -0700 Cc: Linux Kernel Mailing List , "open list:MEMORY MANAGEMENT" , Dan Williams , Ross Zwisler , Linus Torvalds , Bernhard Held , Adam Borowski , Andrea Arcangeli , =?utf-8?B?UmFkaW0gS3LEjW3DocWZ?= , Wanpeng Li , Paolo Bonzini , Takashi Iwai , Mike Galbraith , "Kirill A . Shutemov" , axie , Andrew Morton Message-Id: References: <20170829235447.10050-1-jglisse@redhat.com> <20170829235447.10050-3-jglisse@redhat.com> <6D58FBE4-5D03-49CC-AAFF-3C1279A5A849@gmail.com> <20170830025910.GB2386@redhat.com> To: Jerome Glisse X-Mailer: Apple Mail (2.3273) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v7U3GsaZ004993 Content-Length: 5791 Lines: 145 Jerome Glisse wrote: > On Tue, Aug 29, 2017 at 07:46:07PM -0700, Nadav Amit wrote: >> Jérôme Glisse wrote: >> >>> Replacing all mmu_notifier_invalidate_page() by mmu_notifier_invalidat_range() >>> and making sure it is bracketed by call to mmu_notifier_invalidate_range_start/ >>> end. >>> >>> Note that because we can not presume the pmd value or pte value we have to >>> assume the worse and unconditionaly report an invalidation as happening. >>> >>> Signed-off-by: Jérôme Glisse >>> Cc: Dan Williams >>> Cc: Ross Zwisler >>> Cc: Linus Torvalds >>> Cc: Bernhard Held >>> Cc: Adam Borowski >>> Cc: Andrea Arcangeli >>> Cc: Radim Krčmář >>> Cc: Wanpeng Li >>> Cc: Paolo Bonzini >>> Cc: Takashi Iwai >>> Cc: Nadav Amit >>> Cc: Mike Galbraith >>> Cc: Kirill A. Shutemov >>> Cc: axie >>> Cc: Andrew Morton >>> --- >>> mm/rmap.c | 44 +++++++++++++++++++++++++++++++++++++++++--- >>> 1 file changed, 41 insertions(+), 3 deletions(-) >>> >>> diff --git a/mm/rmap.c b/mm/rmap.c >>> index c8993c63eb25..da97ed525088 100644 >>> --- a/mm/rmap.c >>> +++ b/mm/rmap.c >>> @@ -887,11 +887,21 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, >>> .address = address, >>> .flags = PVMW_SYNC, >>> }; >>> + unsigned long start = address, end; >>> int *cleaned = arg; >>> >>> + /* >>> + * We have to assume the worse case ie pmd for invalidation. Note that >>> + * the page can not be free from this function. >>> + */ >>> + end = min(vma->vm_end, (start & PMD_MASK) + PMD_SIZE); >>> + mmu_notifier_invalidate_range_start(vma->vm_mm, start, end); >>> + >>> while (page_vma_mapped_walk(&pvmw)) { >>> + unsigned long cstart, cend; >>> int ret = 0; >>> - address = pvmw.address; >>> + >>> + cstart = address = pvmw.address; >>> if (pvmw.pte) { >>> pte_t entry; >>> pte_t *pte = pvmw.pte; >>> @@ -904,6 +914,7 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, >>> entry = pte_wrprotect(entry); >>> entry = pte_mkclean(entry); >>> set_pte_at(vma->vm_mm, address, pte, entry); >>> + cend = cstart + PAGE_SIZE; >>> ret = 1; >>> } else { >>> #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE >>> @@ -918,6 +929,8 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, >>> entry = pmd_wrprotect(entry); >>> entry = pmd_mkclean(entry); >>> set_pmd_at(vma->vm_mm, address, pmd, entry); >>> + cstart &= PMD_MASK; >>> + cend = cstart + PMD_SIZE; >>> ret = 1; >>> #else >>> /* unexpected pmd-mapped page? */ >>> @@ -926,11 +939,13 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, >>> } >>> >>> if (ret) { >>> - mmu_notifier_invalidate_page(vma->vm_mm, address); >>> + mmu_notifier_invalidate_range(vma->vm_mm, cstart, cend); >>> (*cleaned)++; >>> } >>> } >>> >>> + mmu_notifier_invalidate_range_end(vma->vm_mm, start, end); >>> + >>> return true; >>> } >>> >>> @@ -1324,6 +1339,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, >>> pte_t pteval; >>> struct page *subpage; >>> bool ret = true; >>> + unsigned long start = address, end; >>> enum ttu_flags flags = (enum ttu_flags)arg; >>> >>> /* munlock has nothing to gain from examining un-locked vmas */ >>> @@ -1335,6 +1351,14 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, >>> flags & TTU_MIGRATION, page); >>> } >>> >>> + /* >>> + * We have to assume the worse case ie pmd for invalidation. Note that >>> + * the page can not be free in this function as call of try_to_unmap() >>> + * must hold a reference on the page. >>> + */ >>> + end = min(vma->vm_end, (start & PMD_MASK) + PMD_SIZE); >>> + mmu_notifier_invalidate_range_start(vma->vm_mm, start, end); >>> + >>> while (page_vma_mapped_walk(&pvmw)) { >>> /* >>> * If the page is mlock()d, we cannot swap it out. >>> @@ -1408,6 +1432,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, >>> set_huge_swap_pte_at(mm, address, >>> pvmw.pte, pteval, >>> vma_mmu_pagesize(vma)); >>> + mmu_notifier_invalidate_range(mm, address, >>> + address + vma_mmu_pagesize(vma)); >> >> I don’t think that the notifier should be called after the PTE is set, but >> after the PTE is cleared, PTE permissions are demoted (e.g., RW->RO) or >> access/dirty bits are cleared. [There is an exception: if the PFN in the PTE >> is changed without clearing the PTE before, but it does not apply here, and >> there is a different notifier for this case.] >> >> Therefore, IIUC, try_to_umap_one() should only call >> mmu_notifier_invalidate_range() after ptep_get_and_clear() and >> ptep_clear_flush() are called. All the other calls to >> mmu_notifier_invalidate_range() in this function can be removed. > > Yes it would simplify the patch, i was trying to optimize for the case > where we restore the pte to its original value after ptep_clear_flush() > or ptep_get_and_clear() as in this case there is no need to invalidate > any secondary page table but that's an overkill optimization that just > add too much complexity. Interesting. Actually, prior to your changes, it seems that the break statements would skip mmu_notifier_invalidate_page() when the PTE is not changed. So why not just change mmu_notifier_invalidate_page() into mmu_notifier_invalidate_range() ? Regards, Nadav