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Commit 99cb0dbd authored by Song Liu's avatar Song Liu Committed by Linus Torvalds
Browse files

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: default avatarSong Liu <songliubraving@fb.com>
Acked-by: default avatarRik van Riel <riel@surriel.com>
Acked-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: default avatarJohannes 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 579c571e

mm/Kconfig

+11 −0
Original line number Diff line number Diff line
@@ -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

mm/filemap.c

+2 −2
Original line number Diff line number Diff line
@@ -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);

	}



	/*

mm/khugepaged.c

+107 −42
Original line number Diff line number Diff line
@@ -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 */
@@ -1348,6 +1356,7 @@ static void collapse_file(struct mm_struct *mm, 
	} while (1);



	__SetPageLocked(new_page);

	if (is_shmem)

		__SetPageSwapBacked(new_page);

	new_page->index = start;

	new_page->mapping = mapping;
@@ -1363,10 +1372,12 @@ static void collapse_file(struct mm_struct *mm, 
		struct page *page = xas_next(&xas);



		VM_BUG_ON(index != xas.xa_index);

		if (is_shmem) {

			if (!page) {

				/*

			 * Stop if extent has been truncated or hole-punched,

			 * and is now completely empty.

				 * Stop if extent has been truncated or

				 * hole-punched, and is now completely

				 * empty.

				 */

				if (index == start) {

					if (!xas_next_entry(&xas, end - 1)) {
@@ -1399,6 +1410,38 @@ static void collapse_file(struct mm_struct *mm, 
				result = SCAN_PAGE_LOCK;

				goto xa_locked;

			}

		} 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_locked;

			} else if (trylock_page(page)) {

				get_page(page);

				xas_unlock_irq(&xas);

			} else {

				result = SCAN_PAGE_LOCK;

				goto xa_locked;

			}

		}



		/*

		 * The page must be locked, so we can drop the i_pages lock
@@ -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 @@ static void collapse_file(struct mm_struct *mm, 
		goto xa_unlocked;

	}



	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 @@ static void collapse_file(struct mm_struct *mm, 


		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);

		count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);



		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);



		/*

		 * Remove pte page tables, so we can re-fault the page as huge.
@@ -1524,6 +1584,8 @@ static void collapse_file(struct mm_struct *mm, 
		/* Something went wrong: roll back page cache changes */

		xas_lock_irq(&xas);

		mapping->nrpages -= nr_none;



		if (is_shmem)

			shmem_uncharge(mapping->host, nr_none);



		xas_set(&xas, start);
@@ -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 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, 
			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);

mm/rmap.c

+8 −4
Original line number Diff line number Diff line
@@ -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);

		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);

		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;