mm,thp: add read-only THP support for (non-shmem) FS

This patch is (hopefully) the first step to enable THP for non-shmem
filesystems.

This patch enables an application to put part of its text sections to THP
via madvise, for example:

    madvise((void *)0x600000, 0x200000, MADV_HUGEPAGE);

We tried to reuse the logic for THP on tmpfs.

Currently, write is not supported for non-shmem THP.  khugepaged will only
process vma with VM_DENYWRITE.  sys_mmap() ignores VM_DENYWRITE requests
(see ksys_mmap_pgoff).  The only way to create vma with VM_DENYWRITE is
execve().  This requirement limits non-shmem THP to text sections.

The next patch will handle writes, which would only happen when the all
the vmas with VM_DENYWRITE are unmapped.

An EXPERIMENTAL config, READ_ONLY_THP_FOR_FS, is added to gate this
feature.

[songliubraving@fb.com: fix build without CONFIG_SHMEM]
Link: http://lkml.kernel.org/r/F53407FB-96CC-42E8-9862-105C92CC2B98@fb.com
[songliubraving@fb.com: fix double unlock in collapse_file()]
Link: http://lkml.kernel.org/r/B960CBFA-8EFC-4DA4-ABC5-1977FFF2CA57@fb.com
Link: http://lkml.kernel.org/r/20190801184244.3169074-7-songliubraving@fb.com
Signed-off-by: Song Liu <songliubraving@fb.com>
Acked-by: Rik van Riel <riel@surriel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/Kconfig b/mm/Kconfig
index f88be1cbcfb26b925d274e40de99ac9145c441f5..a5dae9a7eb510af8f5ae45ae5fc91d2c53a57a91 100644 (file)
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -712,6 +712,17 @@ config GUP_BENCHMARK
 config GUP_GET_PTE_LOW_HIGH
        bool
 
+config READ_ONLY_THP_FOR_FS
+       bool "Read-only THP for filesystems (EXPERIMENTAL)"
+       depends on TRANSPARENT_HUGE_PAGECACHE && SHMEM
+
+       help
+         Allow khugepaged to put read-only file-backed pages in THP.
+
+         This is marked experimental because it is a new feature. Write
+         support of file THPs will be developed in the next few release
+         cycles.
+
 config ARCH_HAS_PTE_SPECIAL
        bool
 

diff --git a/mm/filemap.c b/mm/filemap.c
index f4d2971abd7c6b188de4fd7c4592c75d1a795a1b..91fe3a08ca4a31cca4ad1bc92733287f87b44437 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -203,8 +203,8 @@ static void unaccount_page_cache_page(struct address_space *mapping,
                __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);
+       } else if (PageTransHuge(page)) {
+               __dec_node_page_state(page, NR_FILE_THPS);
        }
 
        /*

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 7e36cc893f25ca4977fcbce08146e0211b3dbbe7..8607c77431b3e03e57cde1e6ae19d8adddc78e06 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -48,6 +48,7 @@ enum scan_result {
        SCAN_CGROUP_CHARGE_FAIL,
        SCAN_EXCEED_SWAP_PTE,
        SCAN_TRUNCATED,
+       SCAN_PAGE_HAS_PRIVATE,
 };
 
 #define CREATE_TRACE_POINTS
@@ -404,7 +405,11 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
            (vm_flags & VM_NOHUGEPAGE) ||
            test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
                return false;
-       if (shmem_file(vma->vm_file)) {
+
+       if (shmem_file(vma->vm_file) ||
+           (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
+            vma->vm_file &&
+            (vm_flags & VM_DENYWRITE))) {
                if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
                        return false;
                return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
@@ -456,8 +461,9 @@ int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
        unsigned long hstart, hend;
 
        /*
-        * khugepaged does not yet work on non-shmem files or special
-        * mappings. And file-private shmem THP is not supported.
+        * khugepaged only supports read-only files for non-shmem files.
+        * khugepaged does not yet work on special mappings. And
+        * file-private shmem THP is not supported.
         */
        if (!hugepage_vma_check(vma, vm_flags))
                return 0;
@@ -1287,12 +1293,12 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
 }
 
 /**
- * collapse_file - collapse small tmpfs/shmem pages into huge one.
+ * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
  *
  * Basic scheme is simple, details are more complex:
  *  - allocate and lock a new huge page;
  *  - scan page cache replacing old pages with the new one
- *    + swap in pages if necessary;
+ *    + swap/gup in pages if necessary;
  *    + fill in gaps;
  *    + keep old pages around in case rollback is required;
  *  - if replacing succeeds:
@@ -1316,7 +1322,9 @@ static void collapse_file(struct mm_struct *mm,
        LIST_HEAD(pagelist);
        XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
        int nr_none = 0, result = SCAN_SUCCEED;
+       bool is_shmem = shmem_file(file);
 
+       VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
        VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
 
        /* Only allocate from the target node */
@@ -1348,7 +1356,8 @@ static void collapse_file(struct mm_struct *mm,
        } while (1);
 
        __SetPageLocked(new_page);
-       __SetPageSwapBacked(new_page);
+       if (is_shmem)
+               __SetPageSwapBacked(new_page);
        new_page->index = start;
        new_page->mapping = mapping;
 
@@ -1363,41 +1372,75 @@ static void collapse_file(struct mm_struct *mm,
                struct page *page = xas_next(&xas);
 
                VM_BUG_ON(index != xas.xa_index);
-               if (!page) {
-                       /*
-                        * Stop if extent has been truncated or hole-punched,
-                        * and is now completely empty.
-                        */
-                       if (index == start) {
-                               if (!xas_next_entry(&xas, end - 1)) {
-                                       result = SCAN_TRUNCATED;
+               if (is_shmem) {
+                       if (!page) {
+                               /*
+                                * Stop if extent has been truncated or
+                                * hole-punched, and is now completely
+                                * empty.
+                                */
+                               if (index == start) {
+                                       if (!xas_next_entry(&xas, end - 1)) {
+                                               result = SCAN_TRUNCATED;
+                                               goto xa_locked;
+                                       }
+                                       xas_set(&xas, index);
+                               }
+                               if (!shmem_charge(mapping->host, 1)) {
+                                       result = SCAN_FAIL;
                                        goto xa_locked;
                                }
-                               xas_set(&xas, index);
+                               xas_store(&xas, new_page);
+                               nr_none++;
+                               continue;
                        }
-                       if (!shmem_charge(mapping->host, 1)) {
-                               result = SCAN_FAIL;
+
+                       if (xa_is_value(page) || !PageUptodate(page)) {
+                               xas_unlock_irq(&xas);
+                               /* swap in or instantiate fallocated page */
+                               if (shmem_getpage(mapping->host, index, &page,
+                                                 SGP_NOHUGE)) {
+                                       result = SCAN_FAIL;
+                                       goto xa_unlocked;
+                               }
+                       } else if (trylock_page(page)) {
+                               get_page(page);
+                               xas_unlock_irq(&xas);
+                       } else {
+                               result = SCAN_PAGE_LOCK;
                                goto xa_locked;
                        }
-                       xas_store(&xas, new_page);
-                       nr_none++;
-                       continue;
-               }
-
-               if (xa_is_value(page) || !PageUptodate(page)) {
-                       xas_unlock_irq(&xas);
-                       /* swap in or instantiate fallocated page */
-                       if (shmem_getpage(mapping->host, index, &page,
-                                               SGP_NOHUGE)) {
+               } else {        /* !is_shmem */
+                       if (!page || xa_is_value(page)) {
+                               xas_unlock_irq(&xas);
+                               page_cache_sync_readahead(mapping, &file->f_ra,
+                                                         file, index,
+                                                         PAGE_SIZE);
+                               /* drain pagevecs to help isolate_lru_page() */
+                               lru_add_drain();
+                               page = find_lock_page(mapping, index);
+                               if (unlikely(page == NULL)) {
+                                       result = SCAN_FAIL;
+                                       goto xa_unlocked;
+                               }
+                       } else if (!PageUptodate(page)) {
+                               xas_unlock_irq(&xas);
+                               wait_on_page_locked(page);
+                               if (!trylock_page(page)) {
+                                       result = SCAN_PAGE_LOCK;
+                                       goto xa_unlocked;
+                               }
+                               get_page(page);
+                       } else if (PageDirty(page)) {
                                result = SCAN_FAIL;
-                               goto xa_unlocked;
+                               goto xa_locked;
+                       } else if (trylock_page(page)) {
+                               get_page(page);
+                               xas_unlock_irq(&xas);
+                       } else {
+                               result = SCAN_PAGE_LOCK;
+                               goto xa_locked;
                        }
-               } else if (trylock_page(page)) {
-                       get_page(page);
-                       xas_unlock_irq(&xas);
-               } else {
-                       result = SCAN_PAGE_LOCK;
-                       goto xa_locked;
                }
 
                /*
@@ -1426,6 +1469,12 @@ static void collapse_file(struct mm_struct *mm,
                        goto out_unlock;
                }
 
+               if (page_has_private(page) &&
+                   !try_to_release_page(page, GFP_KERNEL)) {
+                       result = SCAN_PAGE_HAS_PRIVATE;
+                       goto out_unlock;
+               }
+
                if (page_mapped(page))
                        unmap_mapping_pages(mapping, index, 1, false);
 
@@ -1463,12 +1512,18 @@ out_unlock:
                goto xa_unlocked;
        }
 
-       __inc_node_page_state(new_page, NR_SHMEM_THPS);
+       if (is_shmem)
+               __inc_node_page_state(new_page, NR_SHMEM_THPS);
+       else
+               __inc_node_page_state(new_page, NR_FILE_THPS);
+
        if (nr_none) {
                struct zone *zone = page_zone(new_page);
 
                __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
-               __mod_node_page_state(zone->zone_pgdat, NR_SHMEM, nr_none);
+               if (is_shmem)
+                       __mod_node_page_state(zone->zone_pgdat,
+                                             NR_SHMEM, nr_none);
        }
 
 xa_locked:
@@ -1506,10 +1561,15 @@ xa_unlocked:
 
                SetPageUptodate(new_page);
                page_ref_add(new_page, HPAGE_PMD_NR - 1);
-               set_page_dirty(new_page);
                mem_cgroup_commit_charge(new_page, memcg, false, true);
+
+               if (is_shmem) {
+                       set_page_dirty(new_page);
+                       lru_cache_add_anon(new_page);
+               } else {
+                       lru_cache_add_file(new_page);
+               }
                count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
-               lru_cache_add_anon(new_page);
 
                /*
                 * Remove pte page tables, so we can re-fault the page as huge.
@@ -1524,7 +1584,9 @@ xa_unlocked:
                /* Something went wrong: roll back page cache changes */
                xas_lock_irq(&xas);
                mapping->nrpages -= nr_none;
-               shmem_uncharge(mapping->host, nr_none);
+
+               if (is_shmem)
+                       shmem_uncharge(mapping->host, nr_none);
 
                xas_set(&xas, start);
                xas_for_each(&xas, page, end - 1) {
@@ -1607,7 +1669,8 @@ static void khugepaged_scan_file(struct mm_struct *mm,
                        break;
                }
 
-               if (page_count(page) != 1 + page_mapcount(page)) {
+               if (page_count(page) !=
+                   1 + page_mapcount(page) + page_has_private(page)) {
                        result = SCAN_PAGE_COUNT;
                        break;
                }
@@ -1713,11 +1776,13 @@ skip:
                        VM_BUG_ON(khugepaged_scan.address < hstart ||
                                  khugepaged_scan.address + HPAGE_PMD_SIZE >
                                  hend);
-                       if (shmem_file(vma->vm_file)) {
+                       if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
                                struct file *file;
                                pgoff_t pgoff = linear_page_index(vma,
                                                khugepaged_scan.address);
-                               if (!shmem_huge_enabled(vma))
+
+                               if (shmem_file(vma->vm_file)
+                                   && !shmem_huge_enabled(vma))
                                        goto skip;
                                file = get_file(vma->vm_file);
                                up_read(&mm->mmap_sem);

diff --git a/mm/rmap.c b/mm/rmap.c
index 26006445c8b520c75d3a5acf21da27132453de15..d9a23bb773bf7997773cb94952fbf73c313a0bf3 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1189,8 +1189,10 @@ 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);
+               if (PageSwapBacked(page))
+                       __inc_node_page_state(page, NR_SHMEM_PMDMAPPED);
+               else
+                       __inc_node_page_state(page, NR_FILE_PMDMAPPED);
        } else {
                if (PageTransCompound(page) && page_mapping(page)) {
                        VM_WARN_ON_ONCE(!PageLocked(page));
@@ -1229,8 +1231,10 @@ 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);
+               if (PageSwapBacked(page))
+                       __dec_node_page_state(page, NR_SHMEM_PMDMAPPED);
+               else
+                       __dec_node_page_state(page, NR_FILE_PMDMAPPED);
        } else {
                if (!atomic_add_negative(-1, &page->_mapcount))
                        goto out;