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Date: Mon, 20 Dec 2021 18:37:30 +0000
From: Matthew Wilcox <willy@...radead.org>
To: David Hildenbrand <david@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Nadav Amit <namit@...are.com>,
Jason Gunthorpe <jgg@...dia.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>,
David Rientjes <rientjes@...gle.com>,
Shakeel Butt <shakeelb@...gle.com>,
John Hubbard <jhubbard@...dia.com>,
Mike Kravetz <mike.kravetz@...cle.com>,
Mike Rapoport <rppt@...ux.ibm.com>,
Yang Shi <shy828301@...il.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
Michal Hocko <mhocko@...nel.org>,
Rik van Riel <riel@...riel.com>,
Roman Gushchin <guro@...com>,
Andrea Arcangeli <aarcange@...hat.com>,
Peter Xu <peterx@...hat.com>,
Donald Dutile <ddutile@...hat.com>,
Christoph Hellwig <hch@....de>,
Oleg Nesterov <oleg@...hat.com>, Jan Kara <jack@...e.cz>,
Linux-MM <linux-mm@...ck.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@...r.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v1 06/11] mm: support GUP-triggered unsharing via
FAULT_FLAG_UNSHARE (!hugetlb)
On Sun, Dec 19, 2021 at 09:12:01PM +0000, Matthew Wilcox wrote:
> Can we get rid of ->mapcount altogether? Three states:
This might be a step in the right direction?
>From f723fb7cf2519428eee75e9e779907f80258f302 Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Date: Mon, 20 Dec 2021 13:24:04 -0500
Subject: [PATCH] mm: reuse_swap_page() no longer needs to return map_swapcount
All callers of reuse_swap_page() currently pass NULL, indicating that
they don't use the painstakingly calculated map_swapcount. That lets
us further remove it from page_trans_huge_map_swapcount() and
page_trans_huge_mapcount().
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
I don't know if this is a helpful patch to add at this point or
whether it will get in the way of David's much more extensive work.
include/linux/mm.h | 10 +++-------
include/linux/swap.h | 6 +++---
mm/huge_memory.c | 32 +++++++++++---------------------
mm/khugepaged.c | 2 +-
mm/memory.c | 2 +-
mm/swapfile.c | 33 +++++++++++----------------------
6 files changed, 30 insertions(+), 55 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a7e4a9e7d807..286eb4155c80 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -840,19 +840,15 @@ static inline int page_mapcount(struct page *page)
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
int total_mapcount(struct page *page);
-int page_trans_huge_mapcount(struct page *page, int *total_mapcount);
+int page_trans_huge_mapcount(struct page *page);
#else
static inline int total_mapcount(struct page *page)
{
return page_mapcount(page);
}
-static inline int page_trans_huge_mapcount(struct page *page,
- int *total_mapcount)
+static inline int page_trans_huge_mapcount(struct page *page)
{
- int mapcount = page_mapcount(page);
- if (total_mapcount)
- *total_mapcount = mapcount;
- return mapcount;
+ return page_mapcount(page);
}
#endif
diff --git a/include/linux/swap.h b/include/linux/swap.h
index d1ea44b31f19..1d38d9475c4d 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -514,7 +514,7 @@ extern int __swp_swapcount(swp_entry_t entry);
extern int swp_swapcount(swp_entry_t entry);
extern struct swap_info_struct *page_swap_info(struct page *);
extern struct swap_info_struct *swp_swap_info(swp_entry_t entry);
-extern bool reuse_swap_page(struct page *, int *);
+extern bool reuse_swap_page(struct page *);
extern int try_to_free_swap(struct page *);
struct backing_dev_info;
extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
@@ -680,8 +680,8 @@ static inline int swp_swapcount(swp_entry_t entry)
return 0;
}
-#define reuse_swap_page(page, total_map_swapcount) \
- (page_trans_huge_mapcount(page, total_map_swapcount) == 1)
+#define reuse_swap_page(page) \
+ (page_trans_huge_mapcount(page) == 1)
static inline int try_to_free_swap(struct page *page)
{
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e5483347291c..6ed86a8f6a5b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1322,7 +1322,7 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf)
* We can only reuse the page if nobody else maps the huge page or it's
* part.
*/
- if (reuse_swap_page(page, NULL)) {
+ if (reuse_swap_page(page)) {
pmd_t entry;
entry = pmd_mkyoung(orig_pmd);
entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
@@ -2542,38 +2542,28 @@ int total_mapcount(struct page *page)
* need full accuracy to avoid breaking page pinning, because
* page_trans_huge_mapcount() is slower than page_mapcount().
*/
-int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
+int page_trans_huge_mapcount(struct page *page)
{
- int i, ret, _total_mapcount, mapcount;
+ int i, ret;
/* hugetlbfs shouldn't call it */
VM_BUG_ON_PAGE(PageHuge(page), page);
- if (likely(!PageTransCompound(page))) {
- mapcount = atomic_read(&page->_mapcount) + 1;
- if (total_mapcount)
- *total_mapcount = mapcount;
- return mapcount;
- }
+ if (likely(!PageTransCompound(page)))
+ return atomic_read(&page->_mapcount) + 1;
page = compound_head(page);
- _total_mapcount = ret = 0;
+ ret = 0;
for (i = 0; i < thp_nr_pages(page); i++) {
- mapcount = atomic_read(&page[i]._mapcount) + 1;
+ int mapcount = atomic_read(&page[i]._mapcount) + 1;
ret = max(ret, mapcount);
- _total_mapcount += mapcount;
}
- if (PageDoubleMap(page)) {
+
+ if (PageDoubleMap(page))
ret -= 1;
- _total_mapcount -= thp_nr_pages(page);
- }
- mapcount = compound_mapcount(page);
- ret += mapcount;
- _total_mapcount += mapcount;
- if (total_mapcount)
- *total_mapcount = _total_mapcount;
- return ret;
+
+ return ret + compound_mapcount(page);
}
/* Racy check whether the huge page can be split */
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index e99101162f1a..11794bdf513a 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -681,7 +681,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
goto out;
}
if (!pte_write(pteval) && PageSwapCache(page) &&
- !reuse_swap_page(page, NULL)) {
+ !reuse_swap_page(page)) {
/*
* Page is in the swap cache and cannot be re-used.
* It cannot be collapsed into a THP.
diff --git a/mm/memory.c b/mm/memory.c
index 8f1de811a1dc..dd85fd07cb24 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3626,7 +3626,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
dec_mm_counter_fast(vma->vm_mm, MM_SWAPENTS);
pte = mk_pte(page, vma->vm_page_prot);
- if ((vmf->flags & FAULT_FLAG_WRITE) && reuse_swap_page(page, NULL)) {
+ if ((vmf->flags & FAULT_FLAG_WRITE) && reuse_swap_page(page)) {
pte = maybe_mkwrite(pte_mkdirty(pte), vma);
vmf->flags &= ~FAULT_FLAG_WRITE;
ret |= VM_FAULT_WRITE;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index e59e08ef46e1..bc0810c3b2a5 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1601,31 +1601,30 @@ static bool page_swapped(struct page *page)
return false;
}
-static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount,
+static int page_trans_huge_map_swapcount(struct page *page,
int *total_swapcount)
{
- int i, map_swapcount, _total_mapcount, _total_swapcount;
+ int i, map_swapcount, _total_swapcount;
unsigned long offset = 0;
struct swap_info_struct *si;
struct swap_cluster_info *ci = NULL;
unsigned char *map = NULL;
- int mapcount, swapcount = 0;
+ int swapcount = 0;
/* hugetlbfs shouldn't call it */
VM_BUG_ON_PAGE(PageHuge(page), page);
if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!PageTransCompound(page))) {
- mapcount = page_trans_huge_mapcount(page, total_mapcount);
if (PageSwapCache(page))
swapcount = page_swapcount(page);
if (total_swapcount)
*total_swapcount = swapcount;
- return mapcount + swapcount;
+ return swapcount + page_trans_huge_mapcount(page);
}
page = compound_head(page);
- _total_mapcount = _total_swapcount = map_swapcount = 0;
+ _total_swapcount = map_swapcount = 0;
if (PageSwapCache(page)) {
swp_entry_t entry;
@@ -1639,8 +1638,7 @@ static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount,
if (map)
ci = lock_cluster(si, offset);
for (i = 0; i < HPAGE_PMD_NR; i++) {
- mapcount = atomic_read(&page[i]._mapcount) + 1;
- _total_mapcount += mapcount;
+ int mapcount = atomic_read(&page[i]._mapcount) + 1;
if (map) {
swapcount = swap_count(map[offset + i]);
_total_swapcount += swapcount;
@@ -1648,15 +1646,9 @@ static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount,
map_swapcount = max(map_swapcount, mapcount + swapcount);
}
unlock_cluster(ci);
- if (PageDoubleMap(page)) {
+ if (PageDoubleMap(page))
map_swapcount -= 1;
- _total_mapcount -= HPAGE_PMD_NR;
- }
- mapcount = compound_mapcount(page);
- map_swapcount += mapcount;
- _total_mapcount += mapcount;
- if (total_mapcount)
- *total_mapcount = _total_mapcount;
+ map_swapcount += compound_mapcount(page);
if (total_swapcount)
*total_swapcount = _total_swapcount;
@@ -1673,17 +1665,14 @@ static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount,
* reuse_swap_page() returns false, but it may be always overwritten
* (see the other implementation for CONFIG_SWAP=n).
*/
-bool reuse_swap_page(struct page *page, int *total_map_swapcount)
+bool reuse_swap_page(struct page *page)
{
- int count, total_mapcount, total_swapcount;
+ int count, total_swapcount;
VM_BUG_ON_PAGE(!PageLocked(page), page);
if (unlikely(PageKsm(page)))
return false;
- count = page_trans_huge_map_swapcount(page, &total_mapcount,
- &total_swapcount);
- if (total_map_swapcount)
- *total_map_swapcount = total_mapcount + total_swapcount;
+ count = page_trans_huge_map_swapcount(page, &total_swapcount);
if (count == 1 && PageSwapCache(page) &&
(likely(!PageTransCompound(page)) ||
/* The remaining swap count will be freed soon */
--
2.33.0
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