Add filemap_huge_fault() to attempt to satisfy page faults on memory-mapped read-only text pages using THP when possible.
Signed-off-by: William Kucharski <[email protected]> --- include/linux/mm.h | 2 + mm/Kconfig | 15 ++ mm/filemap.c | 398 +++++++++++++++++++++++++++++++++++++++++++-- mm/huge_memory.c | 3 + mm/mmap.c | 39 ++++- mm/rmap.c | 4 +- mm/vmscan.c | 2 +- 7 files changed, 446 insertions(+), 17 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 0334ca97c584..2a5311721739 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2433,6 +2433,8 @@ extern void truncate_inode_pages_final(struct address_space *); /* generic vm_area_ops exported for stackable file systems */ extern vm_fault_t filemap_fault(struct vm_fault *vmf); +extern vm_fault_t filemap_huge_fault(struct vm_fault *vmf, + enum page_entry_size pe_size); extern void filemap_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff); extern vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf); diff --git a/mm/Kconfig b/mm/Kconfig index 56cec636a1fc..2debaded0e4d 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -736,4 +736,19 @@ config ARCH_HAS_PTE_SPECIAL config ARCH_HAS_HUGEPD bool +config RO_EXEC_FILEMAP_HUGE_FAULT_THP + bool "read-only exec filemap_huge_fault THP support (EXPERIMENTAL)" + depends on TRANSPARENT_HUGE_PAGECACHE && SHMEM + + help + Introduce filemap_huge_fault() to automatically map executable + read-only pages of mapped files of suitable size and alignment + using THP if possible. + + This is marked experimental because it is a new feature and is + dependent upon filesystmes implementing readpages() in a way + that will recognize large THP pages and read file content to + them without polluting the pagecache with PAGESIZE pages due + to readahead. + endmenu diff --git a/mm/filemap.c b/mm/filemap.c index 38b46fc00855..5947d432a4e6 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -199,13 +199,12 @@ static void unaccount_page_cache_page(struct address_space *mapping, nr = hpage_nr_pages(page); __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr); - if (PageSwapBacked(page)) { + + if (PageSwapBacked(page)) __mod_node_page_state(page_pgdat(page), NR_SHMEM, -nr); - if (PageTransHuge(page)) - __dec_node_page_state(page, NR_SHMEM_THPS); - } else { - VM_BUG_ON_PAGE(PageTransHuge(page), page); - } + + if (PageTransHuge(page)) + __dec_node_page_state(page, NR_SHMEM_THPS); /* * At this point page must be either written or cleaned by @@ -303,6 +302,9 @@ static void page_cache_delete_batch(struct address_space *mapping, break; if (xa_is_value(page)) continue; + +VM_BUG_ON_PAGE(xa_is_internal(page), page); + if (!tail_pages) { /* * Some page got inserted in our range? Skip it. We @@ -315,6 +317,11 @@ static void page_cache_delete_batch(struct address_space *mapping, continue; } WARN_ON_ONCE(!PageLocked(page)); + + /* + * If a THP is in the page cache, set the succeeding + * cache entries for the PMD-sized page to NULL. + */ if (PageTransHuge(page) && !PageHuge(page)) tail_pages = HPAGE_PMD_NR - 1; page->mapping = NULL; @@ -324,8 +331,6 @@ static void page_cache_delete_batch(struct address_space *mapping, */ i++; } else { - VM_BUG_ON_PAGE(page->index + HPAGE_PMD_NR - tail_pages - != pvec->pages[i]->index, page); tail_pages--; } xas_store(&xas, NULL); @@ -881,7 +886,10 @@ static int __add_to_page_cache_locked(struct page *page, mapping->nrpages++; /* hugetlb pages do not participate in page cache accounting */ - if (!huge) + if (PageTransHuge(page) && !huge) + __mod_node_page_state(page_pgdat(page), + NR_FILE_PAGES, HPAGE_PMD_NR); + else __inc_node_page_state(page, NR_FILE_PAGES); unlock: xas_unlock_irq(&xas); @@ -1663,7 +1671,8 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset, no_page: if (!page && (fgp_flags & FGP_CREAT)) { int err; - if ((fgp_flags & FGP_WRITE) && mapping_cap_account_dirty(mapping)) + if ((fgp_flags & FGP_WRITE) && + mapping_cap_account_dirty(mapping)) gfp_mask |= __GFP_WRITE; if (fgp_flags & FGP_NOFS) gfp_mask &= ~__GFP_FS; @@ -2643,6 +2652,372 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) } EXPORT_SYMBOL(filemap_fault); +#ifdef CONFIG_RO_EXEC_FILEMAP_HUGE_FAULT_THP +/* + * There is a change coming to store only the head page of a compound page in + * the head cache. + * + * When that change is present in the kernel, remove this #define + */ +#define PAGE_CACHE_STORE_COMPOUND_TAIL_PAGES + +/* + * Check for an entry in the page cache which would conflict with the address + * range we wish to map using a THP or is otherwise unusable to map a large + * cached page. + * + * The routine will return true if a usable page is found in the page cache + * (and *pagep will be set to the address of the cached page), or if no + * cached page is found (and *pagep will be set to NULL). + */ +static bool +filemap_huge_check_pagecache_usable(struct xa_state *xas, + struct page **pagep, pgoff_t hindex, pgoff_t hindex_max) +{ + struct page *page; + + while (1) { + xas_set(xas, hindex); + page = xas_find(xas, hindex_max); + + if (xas_retry(xas, page)) + continue; + + /* + * A found entry is unusable if: + * + the entry is an Xarray value, not a pointer + * + the entry is an internal Xarray node + * + the entry is not a compound page + * + the order of the compound page is < HPAGE_PMD_ORDER + * + the page index is not what we expect it to be + */ + if (!page) + break; + + if (xa_is_value(page) || xa_is_internal(page)) + return false; + +#ifdef PAGE_CACHE_STORE_COMPOUND_TAIL_PAGES + if ((!PageCompound(page)) || (page != compound_head(page))) +#else + if (!PageCompound(page)) +#endif + return false; + + if (compound_order(page) < HPAGE_PMD_ORDER) + return false; + + if (page->index != hindex) + return false; + + break; + } + + *pagep = page; + return true; +} + +/** + * filemap_huge_fault - read in file data for page fault handling to THP + * @vmf: struct vm_fault containing details of the fault + * @pe_size: large page size to map, currently this must be PE_SIZE_PMD + * + * filemap_huge_fault() is invoked via the vma operations vector for a + * mapped memory region to read in file data to a transparent huge page during + * a page fault. + * + * If for any reason we can't allocate a THP, map it or add it to the page + * cache, VM_FAULT_FALLBACK will be returned which will cause the fault + * handler to try mapping the page using a PAGESIZE page, usually via + * filemap_fault() if so speicifed in the vma operations vector. + * + * Returns either VM_FAULT_FALLBACK or the result of calling allcc_set_pte() + * to map the new THP. + * + * NOTE: This routine depends upon the file system's readpage routine as + * specified in the address space operations vector to recognize when it + * is being passed a large page and to read the approprate amount of data + * in full and without polluting the page cache for the large page itself + * with PAGESIZE pages to perform a buffered read or to pollute what + * would be the page cache space for any succeeding pages with PAGESIZE + * pages due to readahead. + * + * It is VITAL that this routine not be enabled without such filesystem + * support. As there is no way to determine how many bytes were read by + * the readpage() operation, if only a PAGESIZE page is read, this routine + * will map the THP containing only the first PAGESIZE bytes of file data + * to satisfy the fault, which is never the result desired. + */ +vm_fault_t filemap_huge_fault(struct vm_fault *vmf, + enum page_entry_size pe_size) +{ + struct file *filp = vmf->vma->vm_file; + struct address_space *mapping = filp->f_mapping; + struct vm_area_struct *vma = vmf->vma; + + unsigned long haddr = vmf->address & HPAGE_PMD_MASK; + pgoff_t hindex = round_down(vmf->pgoff, HPAGE_PMD_NR); + pgoff_t hindex_max = hindex + HPAGE_PMD_NR - 1; + + struct page *cached_page, *hugepage; + struct page *new_page = NULL; + + vm_fault_t ret = VM_FAULT_FALLBACK; + unsigned long nr; + + int error; + bool retry_lookup = true; + + XA_STATE_ORDER(xas, &mapping->i_pages, hindex, HPAGE_PMD_ORDER); + + /* + * Return VM_FAULT_FALLBACK if: + * + * + pe_size != PE_SIZE_PMD + * + FAULT_FLAG_WRITE is set in vmf->flags + * + vma isn't aligned to allow a PMD mapping + * + PMD would extend beyond the end of the vma + */ + if (pe_size != PE_SIZE_PMD || (vmf->flags & FAULT_FLAG_WRITE) || + (haddr < vma->vm_start || + ((haddr + HPAGE_PMD_SIZE) > vma->vm_end))) + return ret; + +retry_lookup: + rcu_read_lock(); + + if (!filemap_huge_check_pagecache_usable(&xas, &cached_page, hindex, + hindex_max)) { + /* found a conflicting entry in the page cache, so fallback */ + rcu_read_unlock(); + return ret; + } else if (cached_page) { + /* found a valid cached page, so map it */ + rcu_read_unlock(); + lock_page(cached_page); + + /* was the cached page truncated while waiting for the lock? */ + if (unlikely(cached_page->mapping != mapping)) { + unlock_page(cached_page); + + /* retry once */ + if (retry_lookup) { + retry_lookup = false; + goto retry_lookup; + } + + return ret; + } + + if (unlikely(!PageUptodate(cached_page))) { + unlock_page(cached_page); + return ret; + } + + VM_BUG_ON_PAGE(cached_page->index != hindex, cached_page); + + hugepage = cached_page; + goto map_huge; + } + + rcu_read_unlock(); + + /* allocate huge THP page in VMA */ + new_page = __page_cache_alloc(vmf->gfp_mask | __GFP_COMP | + __GFP_NOWARN | __GFP_NORETRY, HPAGE_PMD_ORDER); + + if (unlikely(!new_page)) + return ret; + + do { + xas_lock_irq(&xas); + xas_set(&xas, hindex); + xas_create_range(&xas); + + if (!(xas_error(&xas))) + break; + + xas_unlock_irq(&xas); + + if (!xas_nomem(&xas, GFP_KERNEL)) { + /* error creating range, so free THP and fallback */ + if (new_page) + put_page(new_page); + + return ret; + } + } while (1); + + /* i_pages is locked here */ + + /* + * Double check that an entry did not sneak into the page cache while + * creating Xarray entries for the new page. + */ + if (!filemap_huge_check_pagecache_usable(&xas, &cached_page, hindex, + hindex_max)) { + /* + * An unusable entry was found, so delete the newly allocated + * page and fallback. + */ + put_page(new_page); + xas_unlock_irq(&xas); + return ret; + } else if (cached_page) { + /* + * A valid large page was found in the page cache, so free the + * newly allocated page and map the cached page instead. + */ + put_page(new_page); + new_page = NULL; + xas_unlock_irq(&xas); + + lock_page(cached_page); + + /* was the cached page truncated while waiting for the lock? */ + if (unlikely(cached_page->mapping != mapping)) { + unlock_page(cached_page); + + /* retry once */ + if (retry_lookup) { + retry_lookup = false; + goto retry_lookup; + } + + return ret; + } + + if (unlikely(!PageUptodate(cached_page))) { + unlock_page(cached_page); + return ret; + } + + VM_BUG_ON_PAGE(cached_page->index != hindex, cached_page); + + hugepage = cached_page; + goto map_huge; + } + + prep_transhuge_page(new_page); + new_page->mapping = mapping; + new_page->index = hindex; + __SetPageLocked(new_page); + + count_vm_event(THP_FILE_ALLOC); + xas_set(&xas, hindex); + + for (nr = 0; nr < HPAGE_PMD_NR; nr++) { +#ifdef PAGE_CACHE_STORE_COMPOUND_TAIL_PAGES + /* + * Store pointers to both head and tail pages of a compound + * page in the page cache. + */ + xas_store(&xas, new_page + nr); +#else + /* + * All entries for a compound page in the page cache should + * point to the head page. + */ + xas_store(&xas, new_page); +#endif + xas_next(&xas); + } + + mapping->nrpages += HPAGE_PMD_NR; + xas_unlock_irq(&xas); + + /* + * The readpage() operation below is expected to fill the large + * page with data without polluting the page cache with + * PAGESIZE entries due to a buffered read and/or readahead(). + * + * A filesystem's vm_operations_struct huge_fault field should + * never point to this routine without such a capability, and + * without it a call to this routine would eventually just + * fall through to the normal fault op anyway. + */ + error = mapping->a_ops->readpage(vmf->vma->vm_file, new_page); + + if (unlikely(error)) { + ret = VM_FAULT_SIGBUS; + goto delete_hugepage_from_page_cache; + } + + if (wait_on_page_locked_killable(new_page)) { + ret = VM_FAULT_SIGSEGV; + goto delete_hugepage_from_page_cache; + } + + if (!PageUptodate(new_page)) { + /* EIO */ + ret = VM_FAULT_SIGBUS; + goto delete_hugepage_from_page_cache; + } + + lock_page(new_page); + + /* did the page get truncated while waiting for the lock? */ + if (unlikely(new_page->mapping != mapping)) { + unlock_page(new_page); + goto delete_hugepage_from_page_cache; + } + + __inc_node_page_state(new_page, NR_SHMEM_THPS); + __mod_node_page_state(page_pgdat(new_page), + NR_FILE_PAGES, HPAGE_PMD_NR); + __mod_node_page_state(page_pgdat(new_page), + NR_SHMEM, HPAGE_PMD_NR); + + hugepage = new_page; + +map_huge: + /* map hugepage at the PMD level */ + + ret = alloc_set_pte(vmf, vmf->memcg, hugepage); + + VM_BUG_ON_PAGE((!(pmd_trans_huge(*vmf->pmd))), hugepage); + VM_BUG_ON_PAGE(!(PageTransHuge(hugepage)), hugepage); + + if (likely(!(ret & VM_FAULT_ERROR))) { + vmf->address = haddr; + vmf->page = hugepage; + + page_ref_add(hugepage, HPAGE_PMD_NR); + count_vm_event(THP_FILE_MAPPED); + } else { + if (new_page) { + __mod_node_page_state(page_pgdat(new_page), + NR_FILE_PAGES, -HPAGE_PMD_NR); + __mod_node_page_state(page_pgdat(new_page), + NR_SHMEM, -HPAGE_PMD_NR); + __dec_node_page_state(new_page, NR_SHMEM_THPS); + +delete_hugepage_from_page_cache: + xas_lock_irq(&xas); + xas_set(&xas, hindex); + + for (nr = 0; nr < HPAGE_PMD_NR; nr++) { + xas_store(&xas, NULL); + xas_next(&xas); + } + + new_page->mapping = NULL; + xas_unlock_irq(&xas); + + mapping->nrpages -= HPAGE_PMD_NR; + unlock_page(new_page); + page_ref_dec(new_page); /* decrement page coche ref */ + put_page(new_page); /* done with page */ + return ret; + } + } + + unlock_page(hugepage); + return ret; +} +EXPORT_SYMBOL(filemap_huge_fault); +#endif + void filemap_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff) { @@ -2925,7 +3300,8 @@ struct page *read_cache_page(struct address_space *mapping, EXPORT_SYMBOL(read_cache_page); /** - * read_cache_page_gfp - read into page cache, using specified page allocation flags. + * read_cache_page_gfp - read into page cache, using specified page allocation + * flags. * @mapping: the page's address_space * @index: the page index * @gfp: the page allocator flags to use if allocating diff --git a/mm/huge_memory.c b/mm/huge_memory.c index de1f15969e27..ea3dbb6fa538 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -544,8 +544,11 @@ unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr, if (addr) goto out; + +#ifndef CONFIG_RO_EXEC_FILEMAP_HUGE_FAULT_THP if (!IS_DAX(filp->f_mapping->host) || !IS_ENABLED(CONFIG_FS_DAX_PMD)) goto out; +#endif addr = __thp_get_unmapped_area(filp, len, off, flags, PMD_SIZE); if (addr) diff --git a/mm/mmap.c b/mm/mmap.c index 7e8c3e8ae75f..d8b3bce71075 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1391,6 +1391,8 @@ unsigned long do_mmap(struct file *file, unsigned long addr, struct mm_struct *mm = current->mm; int pkey = 0; + unsigned long vm_maywrite = VM_MAYWRITE; + *populate = 0; if (!len) @@ -1426,10 +1428,41 @@ unsigned long do_mmap(struct file *file, unsigned long addr, if (mm->map_count > sysctl_max_map_count) return -ENOMEM; - /* Obtain the address to map to. we verify (or select) it and ensure + /* + * Obtain the address to map to. we verify (or select) it and ensure * that it represents a valid section of the address space. */ - addr = get_unmapped_area(file, addr, len, pgoff, flags); + +#ifdef CONFIG_RO_EXEC_FILEMAP_HUGE_FAULT_THP + /* + * If THP is enabled, it's a read-only executable that is + * MAP_PRIVATE mapped, the length is larger than a PMD page + * and either it's not a MAP_FIXED mapping or the passed address is + * properly aligned for a PMD page, attempt to get an appropriate + * address at which to map a PMD-sized THP page, otherwise call the + * normal routine. + */ + if ((prot & PROT_READ) && (prot & PROT_EXEC) && + (!(prot & PROT_WRITE)) && (flags & MAP_PRIVATE) && + (!(flags & MAP_FIXED)) && len >= HPAGE_PMD_SIZE) { + addr = thp_get_unmapped_area(file, addr, len, pgoff, flags); + + if (addr && (!(addr & ~HPAGE_PMD_MASK))) { + /* + * If we got a suitable THP mapping address, shut off + * VM_MAYWRITE for the region, since it's never what + * we would want. + */ + vm_maywrite = 0; + } else + addr = get_unmapped_area(file, addr, len, pgoff, flags); + } else { +#endif + addr = get_unmapped_area(file, addr, len, pgoff, flags); +#ifdef CONFIG_RO_EXEC_FILEMAP_HUGE_FAULT_THP + } +#endif + if (offset_in_page(addr)) return addr; @@ -1451,7 +1484,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr, * of the memory object, so we don't do any here. */ vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) | - mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC; + mm->def_flags | VM_MAYREAD | vm_maywrite | VM_MAYEXEC; if (flags & MAP_LOCKED) if (!can_do_mlock()) diff --git a/mm/rmap.c b/mm/rmap.c index 003377e24232..aacc6e330329 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1192,7 +1192,7 @@ void page_add_file_rmap(struct page *page, bool compound) } if (!atomic_inc_and_test(compound_mapcount_ptr(page))) goto out; - VM_BUG_ON_PAGE(!PageSwapBacked(page), page); + __inc_node_page_state(page, NR_SHMEM_PMDMAPPED); } else { if (PageTransCompound(page) && page_mapping(page)) { @@ -1232,7 +1232,7 @@ static void page_remove_file_rmap(struct page *page, bool compound) } if (!atomic_add_negative(-1, compound_mapcount_ptr(page))) goto out; - VM_BUG_ON_PAGE(!PageSwapBacked(page), page); + __dec_node_page_state(page, NR_SHMEM_PMDMAPPED); } else { if (!atomic_add_negative(-1, &page->_mapcount)) diff --git a/mm/vmscan.c b/mm/vmscan.c index a6c5d0b28321..47a19c59c9a2 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -930,7 +930,7 @@ static int __remove_mapping(struct address_space *mapping, struct page *page, * Note that if SetPageDirty is always performed via set_page_dirty, * and thus under the i_pages lock, then this ordering is not required. */ - if (unlikely(PageTransHuge(page)) && PageSwapCache(page)) + if (unlikely(PageTransHuge(page))) refcount = 1 + HPAGE_PMD_NR; else refcount = 2; -- 2.21.0
