diff options
| -rw-r--r-- | Documentation/mm/transhuge.rst | 7 | ||||
| -rw-r--r-- | include/linux/mm.h | 19 | ||||
| -rw-r--r-- | include/linux/rmap.h | 13 | ||||
| -rw-r--r-- | mm/page_alloc.c | 2 | ||||
| -rw-r--r-- | mm/rmap.c | 121 |
5 files changed, 51 insertions, 111 deletions
diff --git a/Documentation/mm/transhuge.rst b/Documentation/mm/transhuge.rst index af4c9d70321d..ec3dc5b04226 100644 --- a/Documentation/mm/transhuge.rst +++ b/Documentation/mm/transhuge.rst @@ -118,15 +118,14 @@ pages: succeeds on tail pages. - map/unmap of PMD entry for the whole compound page increment/decrement - ->compound_mapcount, stored in the first tail page of the compound page. + ->compound_mapcount, stored in the first tail page of the compound page; + and also increment/decrement ->subpages_mapcount (also in the first tail) + by COMPOUND_MAPPED when compound_mapcount goes from -1 to 0 or 0 to -1. - map/unmap of sub-pages with PTE entry increment/decrement ->_mapcount on relevant sub-page of the compound page, and also increment/decrement ->subpages_mapcount, stored in first tail page of the compound page, when _mapcount goes from -1 to 0 or 0 to -1: counting sub-pages mapped by PTE. - In order to have race-free accounting of sub-pages mapped, changes to - sub-page ->_mapcount, ->subpages_mapcount and ->compound_mapcount are - are all locked by bit_spin_lock of PG_locked in the first tail ->flags. split_huge_page internally has to distribute the refcounts in the head page to the tail pages before clearing all PG_head/tail bits from the page diff --git a/include/linux/mm.h b/include/linux/mm.h index 84fb91f6f56e..d33639be3db3 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -837,12 +837,21 @@ static inline int head_compound_mapcount(struct page *head) } /* + * If a 16GB hugetlb page were mapped by PTEs of all of its 4kB sub-pages, + * its subpages_mapcount would be 0x400000: choose the COMPOUND_MAPPED bit + * above that range, instead of 2*(PMD_SIZE/PAGE_SIZE). Hugetlb currently + * leaves subpages_mapcount at 0, but avoid surprise if it participates later. + */ +#define COMPOUND_MAPPED 0x800000 +#define SUBPAGES_MAPPED (COMPOUND_MAPPED - 1) + +/* * Number of sub-pages mapped by PTE, does not include compound mapcount. * Must be called only on head of compound page. */ static inline int head_subpages_mapcount(struct page *head) { - return atomic_read(subpages_mapcount_ptr(head)); + return atomic_read(subpages_mapcount_ptr(head)) & SUBPAGES_MAPPED; } /* @@ -902,8 +911,12 @@ static inline int total_mapcount(struct page *page) static inline bool folio_large_is_mapped(struct folio *folio) { - return atomic_read(folio_mapcount_ptr(folio)) + - atomic_read(folio_subpages_mapcount_ptr(folio)) >= 0; + /* + * Reading folio_mapcount_ptr() below could be omitted if hugetlb + * participated in incrementing subpages_mapcount when compound mapped. + */ + return atomic_read(folio_subpages_mapcount_ptr(folio)) > 0 || + atomic_read(folio_mapcount_ptr(folio)) >= 0; } /** diff --git a/include/linux/rmap.h b/include/linux/rmap.h index 5dadb9a3e010..bd3504d11b15 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -204,15 +204,14 @@ void hugepage_add_anon_rmap(struct page *, struct vm_area_struct *, void hugepage_add_new_anon_rmap(struct page *, struct vm_area_struct *, unsigned long address); -void page_dup_compound_rmap(struct page *page); +static inline void __page_dup_rmap(struct page *page, bool compound) +{ + atomic_inc(compound ? compound_mapcount_ptr(page) : &page->_mapcount); +} static inline void page_dup_file_rmap(struct page *page, bool compound) { - /* Is page being mapped by PTE? */ - if (likely(!compound)) - atomic_inc(&page->_mapcount); - else - page_dup_compound_rmap(page); + __page_dup_rmap(page, compound); } /** @@ -261,7 +260,7 @@ static inline int page_try_dup_anon_rmap(struct page *page, bool compound, * the page R/O into both processes. */ dup: - page_dup_file_rmap(page, compound); + __page_dup_rmap(page, compound); return 0; } diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 0705917ddf54..c33b6963c2d7 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1330,7 +1330,7 @@ static int free_tail_pages_check(struct page *head_page, struct page *page) bad_page(page, "nonzero compound_mapcount"); goto out; } - if (unlikely(head_subpages_mapcount(head_page))) { + if (unlikely(atomic_read(subpages_mapcount_ptr(head_page)))) { bad_page(page, "nonzero subpages_mapcount"); goto out; } diff --git a/mm/rmap.c b/mm/rmap.c index e813785da613..459dc1c44d8a 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1085,38 +1085,6 @@ int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff, return page_vma_mkclean_one(&pvmw); } -struct compound_mapcounts { - unsigned int compound_mapcount; - unsigned int subpages_mapcount; -}; - -/* - * lock_compound_mapcounts() first locks, then copies subpages_mapcount and - * compound_mapcount from head[1].compound_mapcount and subpages_mapcount, - * converting from struct page's internal representation to logical count - * (that is, adding 1 to compound_mapcount to hide its offset by -1). - */ -static void lock_compound_mapcounts(struct page *head, - struct compound_mapcounts *local) -{ - bit_spin_lock(PG_locked, &head[1].flags); - local->compound_mapcount = atomic_read(compound_mapcount_ptr(head)) + 1; - local->subpages_mapcount = atomic_read(subpages_mapcount_ptr(head)); -} - -/* - * After caller has updated subpage._mapcount, local subpages_mapcount and - * local compound_mapcount, as necessary, unlock_compound_mapcounts() converts - * and copies them back to the compound head[1] fields, and then unlocks. - */ -static void unlock_compound_mapcounts(struct page *head, - struct compound_mapcounts *local) -{ - atomic_set(compound_mapcount_ptr(head), local->compound_mapcount - 1); - atomic_set(subpages_mapcount_ptr(head), local->subpages_mapcount); - bit_spin_unlock(PG_locked, &head[1].flags); -} - int total_compound_mapcount(struct page *head) { int mapcount = head_compound_mapcount(head); @@ -1140,34 +1108,6 @@ int total_compound_mapcount(struct page *head) return mapcount; } -/* - * page_dup_compound_rmap(), used when copying mm, - * provides a simple example of using lock_ and unlock_compound_mapcounts(). - */ -void page_dup_compound_rmap(struct page *head) -{ - struct compound_mapcounts mapcounts; - - /* - * Hugetlb pages could use lock_compound_mapcounts(), like THPs do; - * but at present they are still being managed by atomic operations: - * which are likely to be somewhat faster, so don't rush to convert - * them over without evaluating the effect. - * - * Note that hugetlb does not call page_add_file_rmap(): - * here is where hugetlb shared page mapcount is raised. - */ - if (PageHuge(head)) { - atomic_inc(compound_mapcount_ptr(head)); - } else if (PageTransHuge(head)) { - /* That test is redundant: it's for safety or to optimize out */ - - lock_compound_mapcounts(head, &mapcounts); - mapcounts.compound_mapcount++; - unlock_compound_mapcounts(head, &mapcounts); - } -} - /** * page_move_anon_rmap - move a page to our anon_vma * @page: the page to move to our anon_vma @@ -1277,7 +1217,7 @@ static void __page_check_anon_rmap(struct page *page, void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address, rmap_t flags) { - struct compound_mapcounts mapcounts; + atomic_t *mapped; int nr = 0, nr_pmdmapped = 0; bool compound = flags & RMAP_COMPOUND; bool first = true; @@ -1290,24 +1230,20 @@ void page_add_anon_rmap(struct page *page, first = atomic_inc_and_test(&page->_mapcount); nr = first; if (first && PageCompound(page)) { - struct page *head = compound_head(page); - - lock_compound_mapcounts(head, &mapcounts); - mapcounts.subpages_mapcount++; - nr = !mapcounts.compound_mapcount; - unlock_compound_mapcounts(head, &mapcounts); + mapped = subpages_mapcount_ptr(compound_head(page)); + nr = atomic_inc_return_relaxed(mapped); + nr = !(nr & COMPOUND_MAPPED); } } else if (PageTransHuge(page)) { /* That test is redundant: it's for safety or to optimize out */ - lock_compound_mapcounts(page, &mapcounts); - first = !mapcounts.compound_mapcount; - mapcounts.compound_mapcount++; + first = atomic_inc_and_test(compound_mapcount_ptr(page)); if (first) { + mapped = subpages_mapcount_ptr(page); + nr = atomic_add_return_relaxed(COMPOUND_MAPPED, mapped); nr_pmdmapped = thp_nr_pages(page); - nr = nr_pmdmapped - mapcounts.subpages_mapcount; + nr = nr_pmdmapped - (nr & SUBPAGES_MAPPED); } - unlock_compound_mapcounts(page, &mapcounts); } VM_BUG_ON_PAGE(!first && (flags & RMAP_EXCLUSIVE), page); @@ -1360,6 +1296,7 @@ void page_add_new_anon_rmap(struct page *page, VM_BUG_ON_PAGE(!PageTransHuge(page), page); /* increment count (starts at -1) */ atomic_set(compound_mapcount_ptr(page), 0); + atomic_set(subpages_mapcount_ptr(page), COMPOUND_MAPPED); nr = thp_nr_pages(page); __mod_lruvec_page_state(page, NR_ANON_THPS, nr); } @@ -1379,7 +1316,7 @@ void page_add_new_anon_rmap(struct page *page, void page_add_file_rmap(struct page *page, struct vm_area_struct *vma, bool compound) { - struct compound_mapcounts mapcounts; + atomic_t *mapped; int nr = 0, nr_pmdmapped = 0; bool first; @@ -1391,24 +1328,20 @@ void page_add_file_rmap(struct page *page, first = atomic_inc_and_test(&page->_mapcount); nr = first; if (first && PageCompound(page)) { - struct page *head = compound_head(page); - - lock_compound_mapcounts(head, &mapcounts); - mapcounts.subpages_mapcount++; - nr = !mapcounts.compound_mapcount; - unlock_compound_mapcounts(head, &mapcounts); + mapped = subpages_mapcount_ptr(compound_head(page)); + nr = atomic_inc_return_relaxed(mapped); + nr = !(nr & COMPOUND_MAPPED); } } else if (PageTransHuge(page)) { /* That test is redundant: it's for safety or to optimize out */ - lock_compound_mapcounts(page, &mapcounts); - first = !mapcounts.compound_mapcount; - mapcounts.compound_mapcount++; + first = atomic_inc_and_test(compound_mapcount_ptr(page)); if (first) { + mapped = subpages_mapcount_ptr(page); + nr = atomic_add_return_relaxed(COMPOUND_MAPPED, mapped); nr_pmdmapped = thp_nr_pages(page); - nr = nr_pmdmapped - mapcounts.subpages_mapcount; + nr = nr_pmdmapped - (nr & SUBPAGES_MAPPED); } - unlock_compound_mapcounts(page, &mapcounts); } if (nr_pmdmapped) @@ -1432,7 +1365,7 @@ void page_add_file_rmap(struct page *page, void page_remove_rmap(struct page *page, struct vm_area_struct *vma, bool compound) { - struct compound_mapcounts mapcounts; + atomic_t *mapped; int nr = 0, nr_pmdmapped = 0; bool last; @@ -1452,24 +1385,20 @@ void page_remove_rmap(struct page *page, last = atomic_add_negative(-1, &page->_mapcount); nr = last; if (last && PageCompound(page)) { - struct page *head = compound_head(page); - - lock_compound_mapcounts(head, &mapcounts); - mapcounts.subpages_mapcount--; - nr = !mapcounts.compound_mapcount; - unlock_compound_mapcounts(head, &mapcounts); + mapped = subpages_mapcount_ptr(compound_head(page)); + nr = atomic_dec_return_relaxed(mapped); + nr = !(nr & COMPOUND_MAPPED); } } else if (PageTransHuge(page)) { /* That test is redundant: it's for safety or to optimize out */ - lock_compound_mapcounts(page, &mapcounts); - mapcounts.compound_mapcount--; - last = !mapcounts.compound_mapcount; + last = atomic_add_negative(-1, compound_mapcount_ptr(page)); if (last) { + mapped = subpages_mapcount_ptr(page); + nr = atomic_sub_return_relaxed(COMPOUND_MAPPED, mapped); nr_pmdmapped = thp_nr_pages(page); - nr = nr_pmdmapped - mapcounts.subpages_mapcount; + nr = nr_pmdmapped - (nr & SUBPAGES_MAPPED); } - unlock_compound_mapcounts(page, &mapcounts); } if (nr_pmdmapped) { |