* [PATCH v2 1/2] mm/filemap: count only the faulting address as a mmap hit
[not found] <20260427165751.746502-1-fujunjie1@qq.com>
@ 2026-04-27 16:57 ` fujunjie
2026-04-27 18:40 ` Matthew Wilcox
2026-04-27 16:57 ` [PATCH v2 2/2] mm/filemap: do not count FAULT_FLAG_TRIED retries as mmap hits fujunjie
1 sibling, 1 reply; 4+ messages in thread
From: fujunjie @ 2026-04-27 16:57 UTC (permalink / raw)
To: Matthew Wilcox, Jan Kara, Andrew Morton
Cc: linux-fsdevel, linux-mm, linux-kernel, Roman Gushchin, Haoran Zhu
filemap_map_pages() reduces file->f_ra.mmap_miss when fault-around maps
folios that are already present in the page cache. That hit accounting
is too generous because fault-around can install PTEs around the
faulting address even though the fault only proves that the faulting
address was accessed.
Move the mmap_miss update back into filemap_map_pages(), drop the
mmap_miss argument from the helper functions, and decrement mmap_miss
only when the helper return value shows that the faulting address was
mapped. Keep the existing workingset-folio behavior unchanged.
Signed-off-by: fujunjie <fujunjie1@qq.com>
---
mm/filemap.c | 55 +++++++++++++++++++++++-----------------------------
1 file changed, 24 insertions(+), 31 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 4e636647100c1..41ffe9036c96e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3747,8 +3747,7 @@ static struct folio *next_uptodate_folio(struct xa_state *xas,
static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
struct folio *folio, unsigned long start,
unsigned long addr, unsigned int nr_pages,
- unsigned long *rss, unsigned short *mmap_miss,
- pgoff_t file_end)
+ unsigned long *rss, pgoff_t file_end)
{
struct address_space *mapping = folio->mapping;
unsigned int ref_from_caller = 1;
@@ -3780,16 +3779,6 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
if (PageHWPoison(page + count))
goto skip;
- /*
- * If there are too many folios that are recently evicted
- * in a file, they will probably continue to be evicted.
- * In such situation, read-ahead is only a waste of IO.
- * Don't decrease mmap_miss in this scenario to make sure
- * we can stop read-ahead.
- */
- if (!folio_test_workingset(folio))
- (*mmap_miss)++;
-
/*
* NOTE: If there're PTE markers, we'll leave them to be
* handled in the specific fault path, and it'll prohibit the
@@ -3836,7 +3825,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
struct folio *folio, unsigned long addr,
- unsigned long *rss, unsigned short *mmap_miss)
+ unsigned long *rss)
{
vm_fault_t ret = 0;
struct page *page = &folio->page;
@@ -3844,10 +3833,6 @@ static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
if (PageHWPoison(page))
goto out;
- /* See comment of filemap_map_folio_range() */
- if (!folio_test_workingset(folio))
- (*mmap_miss)++;
-
/*
* NOTE: If there're PTE markers, we'll leave them to be
* handled in the specific fault path, and it'll prohibit
@@ -3882,7 +3867,6 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
vm_fault_t ret = 0;
unsigned long rss = 0;
unsigned int nr_pages = 0, folio_type;
- unsigned short mmap_miss = 0, mmap_miss_saved;
/*
* Recalculate end_pgoff based on file_end before calling
@@ -3921,6 +3905,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
folio_type = mm_counter_file(folio);
do {
unsigned long end;
+ vm_fault_t map_ret;
addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
vmf->pte += xas.xa_index - last_pgoff;
@@ -3928,13 +3913,27 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
end = folio_next_index(folio) - 1;
nr_pages = min(end, end_pgoff) - xas.xa_index + 1;
- if (!folio_test_large(folio))
- ret |= filemap_map_order0_folio(vmf,
- folio, addr, &rss, &mmap_miss);
- else
- ret |= filemap_map_folio_range(vmf, folio,
- xas.xa_index - folio->index, addr,
- nr_pages, &rss, &mmap_miss, file_end);
+ if (!folio_test_large(folio)) {
+ map_ret = filemap_map_order0_folio(vmf, folio, addr,
+ &rss);
+ } else {
+ unsigned long start = xas.xa_index - folio->index;
+
+ map_ret = filemap_map_folio_range(vmf, folio, start,
+ addr, nr_pages, &rss,
+ file_end);
+ }
+ ret |= map_ret;
+
+ if ((map_ret & VM_FAULT_NOPAGE) &&
+ !folio_test_workingset(folio)) {
+ unsigned short mmap_miss;
+
+ mmap_miss = READ_ONCE(file->f_ra.mmap_miss);
+ if (mmap_miss)
+ WRITE_ONCE(file->f_ra.mmap_miss,
+ mmap_miss - 1);
+ }
folio_unlock(folio);
} while ((folio = next_uptodate_folio(&xas, mapping, end_pgoff)) != NULL);
@@ -3944,12 +3943,6 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
out:
rcu_read_unlock();
- mmap_miss_saved = READ_ONCE(file->f_ra.mmap_miss);
- if (mmap_miss >= mmap_miss_saved)
- WRITE_ONCE(file->f_ra.mmap_miss, 0);
- else
- WRITE_ONCE(file->f_ra.mmap_miss, mmap_miss_saved - mmap_miss);
-
return ret;
}
EXPORT_SYMBOL(filemap_map_pages);
--
2.34.1
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