| Message ID | 20240129143221.263763-7-david@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/memory: optimize unmap/zap with PTE-mapped THP | expand |
On 29/01/2024 14:32, David Hildenbrand wrote: > Nowadays, encoded pages are only used in mmu_gather handling. Let's > update the documentation, and define ENCODED_PAGE_BIT_DELAY_RMAP. While at > it, rename ENCODE_PAGE_BITS to ENCODED_PAGE_BITS. > > If encoded page pointers would ever be used in other context again, we'd > likely want to change the defines to reflect their context (e.g., > ENCODED_PAGE_FLAG_MMU_GATHER_DELAY_RMAP). For now, let's keep it simple. > > This is a preparation for using the remaining spare bit to indicate that > the next item in an array of encoded pages is a "nr_pages" argument and > not an encoded page. > > Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> > --- > include/linux/mm_types.h | 17 +++++++++++------ > mm/mmu_gather.c | 5 +++-- > 2 files changed, 14 insertions(+), 8 deletions(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 8b611e13153e..1b89eec0d6df 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -210,8 +210,8 @@ struct page { > * > * An 'encoded_page' pointer is a pointer to a regular 'struct page', but > * with the low bits of the pointer indicating extra context-dependent > - * information. Not super-common, but happens in mmu_gather and mlock > - * handling, and this acts as a type system check on that use. > + * information. Only used in mmu_gather handling, and this acts as a type > + * system check on that use. > * > * We only really have two guaranteed bits in general, although you could > * play with 'struct page' alignment (see CONFIG_HAVE_ALIGNED_STRUCT_PAGE) > @@ -220,21 +220,26 @@ struct page { > * Use the supplied helper functions to endcode/decode the pointer and bits. > */ > struct encoded_page; > -#define ENCODE_PAGE_BITS 3ul > + > +#define ENCODED_PAGE_BITS 3ul > + > +/* Perform rmap removal after we have flushed the TLB. */ > +#define ENCODED_PAGE_BIT_DELAY_RMAP 1ul > + > static __always_inline struct encoded_page *encode_page(struct page *page, unsigned long flags) > { > - BUILD_BUG_ON(flags > ENCODE_PAGE_BITS); > + BUILD_BUG_ON(flags > ENCODED_PAGE_BITS); > return (struct encoded_page *)(flags | (unsigned long)page); > } > > static inline unsigned long encoded_page_flags(struct encoded_page *page) > { > - return ENCODE_PAGE_BITS & (unsigned long)page; > + return ENCODED_PAGE_BITS & (unsigned long)page; > } > > static inline struct page *encoded_page_ptr(struct encoded_page *page) > { > - return (struct page *)(~ENCODE_PAGE_BITS & (unsigned long)page); > + return (struct page *)(~ENCODED_PAGE_BITS & (unsigned long)page); > } > > /* > diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c > index ac733d81b112..6540c99c6758 100644 > --- a/mm/mmu_gather.c > +++ b/mm/mmu_gather.c > @@ -53,7 +53,7 @@ static void tlb_flush_rmap_batch(struct mmu_gather_batch *batch, struct vm_area_ > for (int i = 0; i < batch->nr; i++) { > struct encoded_page *enc = batch->encoded_pages[i]; > > - if (encoded_page_flags(enc)) { > + if (encoded_page_flags(enc) & ENCODED_PAGE_BIT_DELAY_RMAP) { > struct page *page = encoded_page_ptr(enc); > folio_remove_rmap_pte(page_folio(page), page, vma); > } > @@ -119,6 +119,7 @@ static void tlb_batch_list_free(struct mmu_gather *tlb) > bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, > bool delay_rmap, int page_size) > { > + int flags = delay_rmap ? ENCODED_PAGE_BIT_DELAY_RMAP : 0; > struct mmu_gather_batch *batch; > > VM_BUG_ON(!tlb->end); > @@ -132,7 +133,7 @@ bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, > * Add the page and check if we are full. If so > * force a flush. > */ > - batch->encoded_pages[batch->nr++] = encode_page(page, delay_rmap); > + batch->encoded_pages[batch->nr++] = encode_page(page, flags); > if (batch->nr == batch->max) { > if (!tlb_next_batch(tlb)) > return true;
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 8b611e13153e..1b89eec0d6df 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -210,8 +210,8 @@ struct page { * * An 'encoded_page' pointer is a pointer to a regular 'struct page', but * with the low bits of the pointer indicating extra context-dependent - * information. Not super-common, but happens in mmu_gather and mlock - * handling, and this acts as a type system check on that use. + * information. Only used in mmu_gather handling, and this acts as a type + * system check on that use. * * We only really have two guaranteed bits in general, although you could * play with 'struct page' alignment (see CONFIG_HAVE_ALIGNED_STRUCT_PAGE) @@ -220,21 +220,26 @@ struct page { * Use the supplied helper functions to endcode/decode the pointer and bits. */ struct encoded_page; -#define ENCODE_PAGE_BITS 3ul + +#define ENCODED_PAGE_BITS 3ul + +/* Perform rmap removal after we have flushed the TLB. */ +#define ENCODED_PAGE_BIT_DELAY_RMAP 1ul + static __always_inline struct encoded_page *encode_page(struct page *page, unsigned long flags) { - BUILD_BUG_ON(flags > ENCODE_PAGE_BITS); + BUILD_BUG_ON(flags > ENCODED_PAGE_BITS); return (struct encoded_page *)(flags | (unsigned long)page); } static inline unsigned long encoded_page_flags(struct encoded_page *page) { - return ENCODE_PAGE_BITS & (unsigned long)page; + return ENCODED_PAGE_BITS & (unsigned long)page; } static inline struct page *encoded_page_ptr(struct encoded_page *page) { - return (struct page *)(~ENCODE_PAGE_BITS & (unsigned long)page); + return (struct page *)(~ENCODED_PAGE_BITS & (unsigned long)page); } /* diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c index ac733d81b112..6540c99c6758 100644 --- a/mm/mmu_gather.c +++ b/mm/mmu_gather.c @@ -53,7 +53,7 @@ static void tlb_flush_rmap_batch(struct mmu_gather_batch *batch, struct vm_area_ for (int i = 0; i < batch->nr; i++) { struct encoded_page *enc = batch->encoded_pages[i]; - if (encoded_page_flags(enc)) { + if (encoded_page_flags(enc) & ENCODED_PAGE_BIT_DELAY_RMAP) { struct page *page = encoded_page_ptr(enc); folio_remove_rmap_pte(page_folio(page), page, vma); } @@ -119,6 +119,7 @@ static void tlb_batch_list_free(struct mmu_gather *tlb) bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, bool delay_rmap, int page_size) { + int flags = delay_rmap ? ENCODED_PAGE_BIT_DELAY_RMAP : 0; struct mmu_gather_batch *batch; VM_BUG_ON(!tlb->end); @@ -132,7 +133,7 @@ bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, * Add the page and check if we are full. If so * force a flush. */ - batch->encoded_pages[batch->nr++] = encode_page(page, delay_rmap); + batch->encoded_pages[batch->nr++] = encode_page(page, flags); if (batch->nr == batch->max) { if (!tlb_next_batch(tlb)) return true;
Nowadays, encoded pages are only used in mmu_gather handling. Let's update the documentation, and define ENCODED_PAGE_BIT_DELAY_RMAP. While at it, rename ENCODE_PAGE_BITS to ENCODED_PAGE_BITS. If encoded page pointers would ever be used in other context again, we'd likely want to change the defines to reflect their context (e.g., ENCODED_PAGE_FLAG_MMU_GATHER_DELAY_RMAP). For now, let's keep it simple. This is a preparation for using the remaining spare bit to indicate that the next item in an array of encoded pages is a "nr_pages" argument and not an encoded page. Signed-off-by: David Hildenbrand <david@redhat.com> --- include/linux/mm_types.h | 17 +++++++++++------ mm/mmu_gather.c | 5 +++-- 2 files changed, 14 insertions(+), 8 deletions(-)