The patch titled
Subject: huge tmpfs: SGP_NOALLOC to stop collapse_file() on race
has been removed from the -mm tree. Its filename was
huge-tmpfs-sgp_noalloc-to-stop-collapse_file-on-race.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: huge tmpfs: SGP_NOALLOC to stop collapse_file() on race
khugepaged's collapse_file() currently uses SGP_NOHUGE to tell
shmem_getpage() not to try allocating a huge page, in the very unlikely
event that a racing hole-punch removes the swapped or fallocated page as
soon as i_pages lock is dropped.
We want to consolidate shmem's huge decisions, removing SGP_HUGE and
SGP_NOHUGE; but cannot quite persuade ourselves that it's okay to regress
the protection in this case - Yang Shi points out that the huge page would
remain indefinitely, charged to root instead of the intended memcg.
collapse_file() should not even allocate a small page in this case: why
proceed if someone is punching a hole? SGP_READ is almost the right flag
here, except that it optimizes away from a fallocated page, with NULL to
tell caller to fill with zeroes (like a hole); whereas collapse_file()'s
sequence relies on using a cache page. Add SGP_NOALLOC just for this.
There are too many consecutive "if (page"s there in shmem_getpage_gfp():
group it better; and fix the outdated "bring it back from swap" comment.
Link: https://lkml.kernel.org/r/1355343b-acf-4653-ef79-6aee40214ac5@xxxxxxxxxx
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/shmem_fs.h | 1 +
mm/khugepaged.c | 2 +-
mm/shmem.c | 29 +++++++++++++++++------------
3 files changed, 19 insertions(+), 13 deletions(-)
--- a/include/linux/shmem_fs.h~huge-tmpfs-sgp_noalloc-to-stop-collapse_file-on-race
+++ a/include/linux/shmem_fs.h
@@ -94,6 +94,7 @@ extern unsigned long shmem_partial_swap_
/* Flag allocation requirements to shmem_getpage */
enum sgp_type {
SGP_READ, /* don't exceed i_size, don't allocate page */
+ SGP_NOALLOC, /* similar, but fail on hole or use fallocated page */
SGP_CACHE, /* don't exceed i_size, may allocate page */
SGP_NOHUGE, /* like SGP_CACHE, but no huge pages */
SGP_HUGE, /* like SGP_CACHE, huge pages preferred */
--- a/mm/khugepaged.c~huge-tmpfs-sgp_noalloc-to-stop-collapse_file-on-race
+++ a/mm/khugepaged.c
@@ -1721,7 +1721,7 @@ static void collapse_file(struct mm_stru
xas_unlock_irq(&xas);
/* swap in or instantiate fallocated page */
if (shmem_getpage(mapping->host, index, &page,
- SGP_NOHUGE)) {
+ SGP_NOALLOC)) {
result = SCAN_FAIL;
goto xa_unlocked;
}
--- a/mm/shmem.c~huge-tmpfs-sgp_noalloc-to-stop-collapse_file-on-race
+++ a/mm/shmem.c
@@ -1854,26 +1854,31 @@ repeat:
return error;
}
- if (page)
+ if (page) {
hindex = page->index;
- if (page && sgp == SGP_WRITE)
- mark_page_accessed(page);
-
- /* fallocated page? */
- if (page && !PageUptodate(page)) {
+ if (sgp == SGP_WRITE)
+ mark_page_accessed(page);
+ if (PageUptodate(page))
+ goto out;
+ /* fallocated page */
if (sgp != SGP_READ)
goto clear;
unlock_page(page);
put_page(page);
- page = NULL;
- hindex = index;
}
- if (page || sgp == SGP_READ)
- goto out;
/*
- * Fast cache lookup did not find it:
- * bring it back from swap or allocate.
+ * SGP_READ: succeed on hole, with NULL page, letting caller zero.
+ * SGP_NOALLOC: fail on hole, with NULL page, letting caller fail.
+ */
+ *pagep = NULL;
+ if (sgp == SGP_READ)
+ return 0;
+ if (sgp == SGP_NOALLOC)
+ return -ENOENT;
+
+ /*
+ * Fast cache lookup and swap lookup did not find it: allocate.
*/
if (vma && userfaultfd_missing(vma)) {
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
