Commit 3f79b187 authored by Kairui Song's avatar Kairui Song Committed by Andrew Morton
Browse files

swapfile: get rid of volatile and avoid redundant read 

Patch series "Clean up and fixes for swap", v2.

This series cleans up some code paths, saves a few cycles and reduces the
object size by a bit.  It also fixes some rare race issue with statistics.


This patch (of 4):

Convert a volatile variable to more readable READ_ONCE.  And this actually
avoids the code from reading the variable twice redundantly when it races.

Link: https://lkml.kernel.org/r/20221219185840.25441-1-ryncsn@gmail.com
Link: https://lkml.kernel.org/r/20221219185840.25441-2-ryncsn@gmail.com


Signed-off-by: default avatarKairui Song <kasong@tencent.com>
Reviewed-by: default avatar"Huang, Ying" <ying.huang@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 497b099d

mm/swapfile.c

+4 −3
Original line number Diff line number Diff line
@@ -1835,13 +1835,13 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, 
	pte_t *pte;

	struct swap_info_struct *si;

	int ret = 0;

	volatile unsigned char *swap_map;



	si = swap_info[type];

	pte = pte_offset_map(pmd, addr);

	do {

		struct folio *folio;

		unsigned long offset;

		unsigned char swp_count;



		if (!is_swap_pte(*pte))

			continue;
@@ -1852,7 +1852,6 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, 


		offset = swp_offset(entry);

		pte_unmap(pte);

		swap_map = &si->swap_map[offset];

		folio = swap_cache_get_folio(entry, vma, addr);

		if (!folio) {

			struct page *page;
@@ -1869,8 +1868,10 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, 
				folio = page_folio(page);

		}

		if (!folio) {

			if (*swap_map == 0 || *swap_map == SWAP_MAP_BAD)

			swp_count = READ_ONCE(si->swap_map[offset]);

			if (swp_count == 0 || swp_count == SWAP_MAP_BAD)

				goto try_next;



			return -ENOMEM;

		}