| Message ID | 20210204145033.136755-4-peterx@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/hugetlb: Early cow on fork, and a few cleanups | expand |
On Thu, Feb 4, 2021 at 6:50 AM Peter Xu <peterx@redhat.com> wrote: > > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1291,6 +1291,27 @@ static inline bool page_maybe_dma_pinned(struct page *page) > GUP_PIN_COUNTING_BIAS; > } > > +static inline bool is_cow_mapping(vm_flags_t flags) > +{ > + return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; > +} Oh, and I just realized: moving this to <linux/mm.h> means that this patch could/should also get rid of - manual copy of this in mm/hugetlb.c: cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; - private #define for the same thing in fs/proc/task_mmu.c #define is_cow_mapping(flags) (((flags) & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE) - manual copy in drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c: bool is_cow_mapping = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; I guess it could be a later cleanup patch too, but maybe best done in this series just to not forget about it. Linus
On Thu, Feb 04, 2021 at 09:54:37AM -0800, Linus Torvalds wrote: > On Thu, Feb 4, 2021 at 6:50 AM Peter Xu <peterx@redhat.com> wrote: > > > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -1291,6 +1291,27 @@ static inline bool page_maybe_dma_pinned(struct page *page) > > GUP_PIN_COUNTING_BIAS; > > } > > > > +static inline bool is_cow_mapping(vm_flags_t flags) > > +{ > > + return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; > > +} > > Oh, and I just realized: moving this to <linux/mm.h> means that this > patch could/should also get rid of > > - manual copy of this in mm/hugetlb.c: > > cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; > > - private #define for the same thing in fs/proc/task_mmu.c > > #define is_cow_mapping(flags) (((flags) & (VM_SHARED | > VM_MAYWRITE)) == VM_MAYWRITE) > > - manual copy in drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c: > > bool is_cow_mapping = > (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; > > I guess it could be a later cleanup patch too, but maybe best done in > this series just to not forget about it. Will do in v3 if there is. Or I'll post a standalone patch to not disturb Gal just in case he's kicked a test. Thanks,
On Thu, Feb 04, 2021 at 09:50:32AM -0500, Peter Xu wrote: > We've got quite a few places (pte, pmd, pud) that explicitly checked against > whether we should break the cow right now during fork(). It's easier to > provide a helper, especially before we work the same thing on hugetlbfs. > > Since we'll reference is_cow_mapping() in mm.h, move it there too. Actually it > suites mm.h more since internal.h is mm/ only, but mm.h is exported to the > whole kernel. With that we should expect another patch to use is_cow_mapping() > whenever we can across the kernel since we do use it quite a lot but it's > always done with raw code against VM_* flags. > > Signed-off-by: Peter Xu <peterx@redhat.com> > include/linux/mm.h | 21 +++++++++++++++++++++ > mm/huge_memory.c | 8 ++------ > mm/internal.h | 5 ----- > mm/memory.c | 7 +------ > 4 files changed, 24 insertions(+), 17 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index ecdf8a8cd6ae..6ea20721d349 100644 > +++ b/include/linux/mm.h > @@ -1291,6 +1291,27 @@ static inline bool page_maybe_dma_pinned(struct page *page) > GUP_PIN_COUNTING_BIAS; > } > > +static inline bool is_cow_mapping(vm_flags_t flags) > +{ It feels a bit more logical to pass in a struct vm_area_struct *' here? Jason
On Thu, Feb 04, 2021 at 07:20:00PM -0400, Jason Gunthorpe wrote: > > +static inline bool is_cow_mapping(vm_flags_t flags) > > +{ > > It feels a bit more logical to pass in a struct vm_area_struct *' here? Agree, but only if I'm adding this as a new function. Though it's a code movement from internal.h to mm.h, so I avoided touching all the users of this function that existed. Thanks,
diff --git a/include/linux/mm.h b/include/linux/mm.h index ecdf8a8cd6ae..6ea20721d349 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1291,6 +1291,27 @@ static inline bool page_maybe_dma_pinned(struct page *page) GUP_PIN_COUNTING_BIAS; } +static inline bool is_cow_mapping(vm_flags_t flags) +{ + return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; +} + +/* + * This should most likely only be called during fork() to see whether we + * should break the cow immediately for a page on the src mm. + */ +static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma, + struct page *page) +{ + if (!is_cow_mapping(vma->vm_flags)) + return false; + + if (!atomic_read(&vma->vm_mm->has_pinned)) + return false; + + return page_maybe_dma_pinned(page); +} + #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) #define SECTION_IN_PAGE_FLAGS #endif diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 9237976abe72..dbff6c7eda67 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1095,9 +1095,7 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, * best effort that the pinned pages won't be replaced by another * random page during the coming copy-on-write. */ - if (unlikely(is_cow_mapping(vma->vm_flags) && - atomic_read(&src_mm->has_pinned) && - page_maybe_dma_pinned(src_page))) { + if (unlikely(page_needs_cow_for_dma(vma, src_page))) { pte_free(dst_mm, pgtable); spin_unlock(src_ptl); spin_unlock(dst_ptl); @@ -1209,9 +1207,7 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm, } /* Please refer to comments in copy_huge_pmd() */ - if (unlikely(is_cow_mapping(vma->vm_flags) && - atomic_read(&src_mm->has_pinned) && - page_maybe_dma_pinned(pud_page(pud)))) { + if (unlikely(page_needs_cow_for_dma(vma, pud_page(pud)))) { spin_unlock(src_ptl); spin_unlock(dst_ptl); __split_huge_pud(vma, src_pud, addr); diff --git a/mm/internal.h b/mm/internal.h index 25d2b2439f19..24eec93d0dac 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -296,11 +296,6 @@ static inline unsigned int buddy_order(struct page *page) */ #define buddy_order_unsafe(page) READ_ONCE(page_private(page)) -static inline bool is_cow_mapping(vm_flags_t flags) -{ - return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; -} - /* * These three helpers classifies VMAs for virtual memory accounting. */ diff --git a/mm/memory.c b/mm/memory.c index feff48e1465a..b2849e1d4aab 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -800,9 +800,6 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma struct mm_struct *src_mm = src_vma->vm_mm; struct page *new_page; - if (!is_cow_mapping(src_vma->vm_flags)) - return 1; - /* * What we want to do is to check whether this page may * have been pinned by the parent process. If so, @@ -816,9 +813,7 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma * the page count. That might give false positives for * for pinning, but it will work correctly. */ - if (likely(!atomic_read(&src_mm->has_pinned))) - return 1; - if (likely(!page_maybe_dma_pinned(page))) + if (likely(!page_needs_cow_for_dma(src_vma, page))) return 1; new_page = *prealloc;
We've got quite a few places (pte, pmd, pud) that explicitly checked against whether we should break the cow right now during fork(). It's easier to provide a helper, especially before we work the same thing on hugetlbfs. Since we'll reference is_cow_mapping() in mm.h, move it there too. Actually it suites mm.h more since internal.h is mm/ only, but mm.h is exported to the whole kernel. With that we should expect another patch to use is_cow_mapping() whenever we can across the kernel since we do use it quite a lot but it's always done with raw code against VM_* flags. Signed-off-by: Peter Xu <peterx@redhat.com> --- include/linux/mm.h | 21 +++++++++++++++++++++ mm/huge_memory.c | 8 ++------ mm/internal.h | 5 ----- mm/memory.c | 7 +------ 4 files changed, 24 insertions(+), 17 deletions(-)