Commit 1fb08ac6 authored by Yang Shi's avatar Yang Shi Committed by Linus Torvalds
Browse files

mm: rmap: make try_to_unmap() void function 

Currently try_to_unmap() return bool value by checking page_mapcount(),
however this may return false positive since page_mapcount() doesn't check
all subpages of compound page.  The total_mapcount() could be used
instead, but its cost is higher since it traverses all subpages.

Actually the most callers of try_to_unmap() don't care about the return
value at all.  So just need check if page is still mapped by page_mapped()
when necessary.  And page_mapped() does bail out early when it finds
mapped subpage.

Link: https://lkml.kernel.org/r/bb27e3fe-6036-b637-5086-272befbfe3da@google.com


Suggested-by: default avatarHugh Dickins <hughd@google.com>
Signed-off-by: default avatarYang Shi <shy828301@gmail.com>
Acked-by: default avatarMinchan Kim <minchan@kernel.org>
Reviewed-by: default avatarShakeel Butt <shakeelb@google.com>
Acked-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Acked-by: default avatarNaoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jue Wang <juew@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Wang Yugui <wangyugui@e16-tech.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cebc774f

include/linux/rmap.h

+1 −1
Original line number Diff line number Diff line
@@ -195,7 +195,7 @@ static inline void page_dup_rmap(struct page *page, bool compound) 
int page_referenced(struct page *, int is_locked,

			struct mem_cgroup *memcg, unsigned long *vm_flags);



bool try_to_unmap(struct page *, enum ttu_flags flags);

void try_to_unmap(struct page *, enum ttu_flags flags);



/* Avoid racy checks */

#define PVMW_SYNC		(1 << 0)

mm/memory-failure.c

+7 −8
Original line number Diff line number Diff line
@@ -1269,7 +1269,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn, 
	enum ttu_flags ttu = TTU_IGNORE_MLOCK;

	struct address_space *mapping;

	LIST_HEAD(tokill);

	bool unmap_success = true;

	bool unmap_success;

	int kill = 1, forcekill;

	struct page *hpage = *hpagep;

	bool mlocked = PageMlocked(hpage);
@@ -1332,7 +1332,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn, 
		collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED);



	if (!PageHuge(hpage)) {

		unmap_success = try_to_unmap(hpage, ttu);

		try_to_unmap(hpage, ttu);

	} else {

		if (!PageAnon(hpage)) {

			/*
@@ -1344,17 +1344,16 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn, 
			 */

			mapping = hugetlb_page_mapping_lock_write(hpage);

			if (mapping) {

				unmap_success = try_to_unmap(hpage,

						     ttu|TTU_RMAP_LOCKED);

				try_to_unmap(hpage, ttu|TTU_RMAP_LOCKED);

				i_mmap_unlock_write(mapping);

			} else {

			} else

				pr_info("Memory failure: %#lx: could not lock mapping for mapped huge page\n", pfn);

				unmap_success = false;

			}

		} else {

			unmap_success = try_to_unmap(hpage, ttu);

			try_to_unmap(hpage, ttu);

		}

	}



	unmap_success = !page_mapped(hpage);

	if (!unmap_success)

		pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n",

		       pfn, page_mapcount(hpage));

mm/rmap.c

+4 −11
Original line number Diff line number Diff line
@@ -1405,7 +1405,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, 
	/*

	 * When racing against e.g. zap_pte_range() on another cpu,

	 * in between its ptep_get_and_clear_full() and page_remove_rmap(),

	 * try_to_unmap() may return false when it is about to become true,

	 * try_to_unmap() may return before page_mapped() has become false,

	 * if page table locking is skipped: use TTU_SYNC to wait for that.

	 */

	if (flags & TTU_SYNC)
@@ -1756,9 +1756,10 @@ static int page_not_mapped(struct page *page) 
 * Tries to remove all the page table entries which are mapping this

 * page, used in the pageout path.  Caller must hold the page lock.

 *

 * If unmap is successful, return true. Otherwise, false.

 * It is the caller's responsibility to check if the page is still

 * mapped when needed (use TTU_SYNC to prevent accounting races).

 */

bool try_to_unmap(struct page *page, enum ttu_flags flags)

void try_to_unmap(struct page *page, enum ttu_flags flags)

{

	struct rmap_walk_control rwc = {

		.rmap_one = try_to_unmap_one,
@@ -1783,14 +1784,6 @@ bool try_to_unmap(struct page *page, enum ttu_flags flags) 
		rmap_walk_locked(page, &rwc);

	else

		rmap_walk(page, &rwc);



	/*

	 * When racing against e.g. zap_pte_range() on another cpu,

	 * in between its ptep_get_and_clear_full() and page_remove_rmap(),

	 * try_to_unmap() may return false when it is about to become true,

	 * if page table locking is skipped: use TTU_SYNC to wait for that.

	 */

	return !page_mapcount(page);

}



/**

mm/vmscan.c

+2 −1
Original line number Diff line number Diff line
@@ -1499,7 +1499,8 @@ static unsigned int shrink_page_list(struct list_head *page_list, 
			if (unlikely(PageTransHuge(page)))

				flags |= TTU_SPLIT_HUGE_PMD;



			if (!try_to_unmap(page, flags)) {

			try_to_unmap(page, flags);

			if (page_mapped(page)) {

				stat->nr_unmap_fail += nr_pages;

				if (!was_swapbacked && PageSwapBacked(page))

					stat->nr_lazyfree_fail += nr_pages;