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Commit 53f79acb authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

mm: mlocking in try_to_unmap_one 



There's contorted mlock/munlock handling in try_to_unmap_anon() and
try_to_unmap_file(), which we'd prefer not to repeat for KSM swapping.
Simplify it by moving it all down into try_to_unmap_one().

One thing is then lost, try_to_munlock()'s distinction between when no vma
holds the page mlocked, and when a vma does mlock it, but we could not get
mmap_sem to set the page flag.  But its only caller takes no interest in
that distinction (and is better testing SWAP_MLOCK anyway), so let's keep
the code simple and return SWAP_AGAIN for both cases.

try_to_unmap_file()'s TTU_MUNLOCK nonlinear handling was particularly
amusing: once unravelled, it turns out to have been choosing between two
different ways of doing the same nothing.  Ah, no, one way was actually
returning SWAP_FAIL when it meant to return SWAP_SUCCESS.

[kosaki.motohiro@jp.fujitsu.com: comment adding to mlocking in try_to_unmap_one]
[akpm@linux-foundation.org: remove test of MLOCK_PAGES]
Signed-off-by: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3ca7b3c5

mm/mlock.c

+1 −1
Original line number Diff line number Diff line
@@ -117,7 +117,7 @@ static void munlock_vma_page(struct page *page) 
			/*

			 * did try_to_unlock() succeed or punt?

			 */

			if (ret == SWAP_SUCCESS || ret == SWAP_AGAIN)

			if (ret != SWAP_MLOCK)

				count_vm_event(UNEVICTABLE_PGMUNLOCKED);



			putback_lru_page(page);

mm/rmap.c

+31 −79
Original line number Diff line number Diff line
@@ -788,6 +788,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, 
			ret = SWAP_MLOCK;

			goto out_unmap;

		}

		if (MLOCK_PAGES && TTU_ACTION(flags) == TTU_MUNLOCK)

			goto out_unmap;

	}

	if (!(flags & TTU_IGNORE_ACCESS)) {

		if (ptep_clear_flush_young_notify(vma, address, pte)) {
@@ -853,12 +855,22 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, 
	} else

		dec_mm_counter(mm, file_rss);





	page_remove_rmap(page);

	page_cache_release(page);



out_unmap:

	pte_unmap_unlock(pte, ptl);



	if (MLOCK_PAGES && ret == SWAP_MLOCK) {

		ret = SWAP_AGAIN;

		if (down_read_trylock(&vma->vm_mm->mmap_sem)) {

			if (vma->vm_flags & VM_LOCKED) {

				mlock_vma_page(page);

				ret = SWAP_MLOCK;

			}

			up_read(&vma->vm_mm->mmap_sem);

		}

	}

out:

	return ret;

}
@@ -980,23 +992,6 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount, 
	return ret;

}



/*

 * common handling for pages mapped in VM_LOCKED vmas

 */

static int try_to_mlock_page(struct page *page, struct vm_area_struct *vma)

{

	int mlocked = 0;



	if (down_read_trylock(&vma->vm_mm->mmap_sem)) {

		if (vma->vm_flags & VM_LOCKED) {

			mlock_vma_page(page);

			mlocked++;	/* really mlocked the page */

		}

		up_read(&vma->vm_mm->mmap_sem);

	}

	return mlocked;

}



/**

 * try_to_unmap_anon - unmap or unlock anonymous page using the object-based

 * rmap method
@@ -1017,42 +1012,19 @@ static int try_to_unmap_anon(struct page *page, enum ttu_flags flags) 
{

	struct anon_vma *anon_vma;

	struct vm_area_struct *vma;

	unsigned int mlocked = 0;

	int ret = SWAP_AGAIN;

	int unlock = TTU_ACTION(flags) == TTU_MUNLOCK;



	if (MLOCK_PAGES && unlikely(unlock))

		ret = SWAP_SUCCESS;	/* default for try_to_munlock() */



	anon_vma = page_lock_anon_vma(page);

	if (!anon_vma)

		return ret;



	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {

		if (MLOCK_PAGES && unlikely(unlock)) {

			if (!((vma->vm_flags & VM_LOCKED) &&

			      page_mapped_in_vma(page, vma)))

				continue;  /* must visit all unlocked vmas */

			ret = SWAP_MLOCK;  /* saw at least one mlocked vma */

		} else {

		ret = try_to_unmap_one(page, vma, flags);

			if (ret == SWAP_FAIL || !page_mapped(page))

		if (ret != SWAP_AGAIN || !page_mapped(page))

			break;

	}

		if (ret == SWAP_MLOCK) {

			mlocked = try_to_mlock_page(page, vma);

			if (mlocked)

				break;	/* stop if actually mlocked page */

		}

	}



	page_unlock_anon_vma(anon_vma);



	if (mlocked)

		ret = SWAP_MLOCK;	/* actually mlocked the page */

	else if (ret == SWAP_MLOCK)

		ret = SWAP_AGAIN;	/* saw VM_LOCKED vma */



	return ret;

}
@@ -1082,42 +1054,27 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags) 
	unsigned long max_nl_cursor = 0;

	unsigned long max_nl_size = 0;

	unsigned int mapcount;

	unsigned int mlocked = 0;

	int unlock = TTU_ACTION(flags) == TTU_MUNLOCK;



	if (MLOCK_PAGES && unlikely(unlock))

		ret = SWAP_SUCCESS;	/* default for try_to_munlock() */



	spin_lock(&mapping->i_mmap_lock);

	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {

		if (MLOCK_PAGES && unlikely(unlock)) {

			if (!((vma->vm_flags & VM_LOCKED) &&

						page_mapped_in_vma(page, vma)))

				continue;	/* must visit all vmas */

			ret = SWAP_MLOCK;

		} else {

		ret = try_to_unmap_one(page, vma, flags);

			if (ret == SWAP_FAIL || !page_mapped(page))

		if (ret != SWAP_AGAIN || !page_mapped(page))

			goto out;

	}

		if (ret == SWAP_MLOCK) {

			mlocked = try_to_mlock_page(page, vma);

			if (mlocked)

				goto out;  /* stop if actually mlocked page */

		}

	}



	if (list_empty(&mapping->i_mmap_nonlinear))

		goto out;



	/*

	 * We don't bother to try to find the munlocked page in nonlinears.

	 * It's costly. Instead, later, page reclaim logic may call

	 * try_to_unmap(TTU_MUNLOCK) and recover PG_mlocked lazily.

	 */

	if (TTU_ACTION(flags) == TTU_MUNLOCK)

		goto out;



	list_for_each_entry(vma, &mapping->i_mmap_nonlinear,

						shared.vm_set.list) {

		if (MLOCK_PAGES && unlikely(unlock)) {

			if (!(vma->vm_flags & VM_LOCKED))

				continue;	/* must visit all vmas */

			ret = SWAP_MLOCK;	/* leave mlocked == 0 */

			goto out;		/* no need to look further */

		}

		if (!MLOCK_PAGES && !(flags & TTU_IGNORE_MLOCK) &&

			(vma->vm_flags & VM_LOCKED))

			continue;
@@ -1159,10 +1116,9 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags) 
			cursor = (unsigned long) vma->vm_private_data;

			while ( cursor < max_nl_cursor &&

				cursor < vma->vm_end - vma->vm_start) {

				ret = try_to_unmap_cluster(cursor, &mapcount,

								vma, page);

				if (ret == SWAP_MLOCK)

					mlocked = 2;	/* to return below */

				if (try_to_unmap_cluster(cursor, &mapcount,

						vma, page) == SWAP_MLOCK)

					ret = SWAP_MLOCK;

				cursor += CLUSTER_SIZE;

				vma->vm_private_data = (void *) cursor;

				if ((int)mapcount <= 0)
@@ -1183,10 +1139,6 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags) 
		vma->vm_private_data = NULL;

out:

	spin_unlock(&mapping->i_mmap_lock);

	if (mlocked)

		ret = SWAP_MLOCK;	/* actually mlocked the page */

	else if (ret == SWAP_MLOCK)

		ret = SWAP_AGAIN;	/* saw VM_LOCKED vma */

	return ret;

}
@@ -1229,7 +1181,7 @@ int try_to_unmap(struct page *page, enum ttu_flags flags) 
 *

 * Return values are:

 *

 * SWAP_SUCCESS	- no vma's holding page mlocked.

 * SWAP_AGAIN	- no vma is holding page mlocked, or,

 * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem

 * SWAP_MLOCK	- page is now mlocked.

 */