The patch titled
Subject: mm/huge_memory: avoid PMD-size page cache if needed
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-huge_memory-avoid-pmd-size-page-cache-if-needed.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-avoid-pmd-size-page-cache-if-needed.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
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------------------------------------------------------
From: Gavin Shan <gshan@xxxxxxxxxx>
Subject: mm/huge_memory: avoid PMD-size page cache if needed
Date: Mon, 15 Jul 2024 10:04:23 +1000
xarray can't support arbitrary page cache size. the largest and supported
page cache size is defined as MAX_PAGECACHE_ORDER by commit 099d90642a71
("mm/filemap: make MAX_PAGECACHE_ORDER acceptable to xarray"). However,
it's possible to have 512MB page cache in the huge memory's collapsing
path on ARM64 system whose base page size is 64KB. 512MB page cache is
breaking the limitation and a warning is raised when the xarray entry is
split as shown in the following example.
[root@dhcp-10-26-1-207 ~]# cat /proc/1/smaps | grep KernelPageSize
KernelPageSize: 64 kB
[root@dhcp-10-26-1-207 ~]# cat /tmp/test.c
:
int main(int argc, char **argv)
{
const char *filename = TEST_XFS_FILENAME;
int fd = 0;
void *buf = (void *)-1, *p;
int pgsize = getpagesize();
int ret = 0;
if (pgsize != 0x10000) {
fprintf(stdout, "System with 64KB base page size is required!\n");
return -EPERM;
}
system("echo 0 > /sys/devices/virtual/bdi/253:0/read_ahead_kb");
system("echo 1 > /proc/sys/vm/drop_caches");
/* Open the xfs file */
fd = open(filename, O_RDONLY);
assert(fd > 0);
/* Create VMA */
buf = mmap(NULL, TEST_MEM_SIZE, PROT_READ, MAP_SHARED, fd, 0);
assert(buf != (void *)-1);
fprintf(stdout, "mapped buffer at 0x%p\n", buf);
/* Populate VMA */
ret = madvise(buf, TEST_MEM_SIZE, MADV_NOHUGEPAGE);
assert(ret == 0);
ret = madvise(buf, TEST_MEM_SIZE, MADV_POPULATE_READ);
assert(ret == 0);
/* Collapse VMA */
ret = madvise(buf, TEST_MEM_SIZE, MADV_HUGEPAGE);
assert(ret == 0);
ret = madvise(buf, TEST_MEM_SIZE, MADV_COLLAPSE);
if (ret) {
fprintf(stdout, "Error %d to madvise(MADV_COLLAPSE)\n", errno);
goto out;
}
/* Split xarray entry. Write permission is needed */
munmap(buf, TEST_MEM_SIZE);
buf = (void *)-1;
close(fd);
fd = open(filename, O_RDWR);
assert(fd > 0);
fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
TEST_MEM_SIZE - pgsize, pgsize);
out:
if (buf != (void *)-1)
munmap(buf, TEST_MEM_SIZE);
if (fd > 0)
close(fd);
return ret;
}
[root@dhcp-10-26-1-207 ~]# gcc /tmp/test.c -o /tmp/test
[root@dhcp-10-26-1-207 ~]# /tmp/test
------------[ cut here ]------------
WARNING: CPU: 25 PID: 7560 at lib/xarray.c:1025 xas_split_alloc+0xf8/0x128
Modules linked in: nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib \
nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct \
nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 \
ip_set rfkill nf_tables nfnetlink vfat fat virtio_balloon drm fuse \
xfs libcrc32c crct10dif_ce ghash_ce sha2_ce sha256_arm64 virtio_net \
sha1_ce net_failover virtio_blk virtio_console failover dimlib virtio_mmio
CPU: 25 PID: 7560 Comm: test Kdump: loaded Not tainted 6.10.0-rc7-gavin+ #9
Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20240524-1.el9 05/24/2024
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : xas_split_alloc+0xf8/0x128
lr : split_huge_page_to_list_to_order+0x1c4/0x780
sp : ffff8000ac32f660
x29: ffff8000ac32f660 x28: ffff0000e0969eb0 x27: ffff8000ac32f6c0
x26: 0000000000000c40 x25: ffff0000e0969eb0 x24: 000000000000000d
x23: ffff8000ac32f6c0 x22: ffffffdfc0700000 x21: 0000000000000000
x20: 0000000000000000 x19: ffffffdfc0700000 x18: 0000000000000000
x17: 0000000000000000 x16: ffffd5f3708ffc70 x15: 0000000000000000
x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
x11: ffffffffffffffc0 x10: 0000000000000040 x9 : ffffd5f3708e692c
x8 : 0000000000000003 x7 : 0000000000000000 x6 : ffff0000e0969eb8
x5 : ffffd5f37289e378 x4 : 0000000000000000 x3 : 0000000000000c40
x2 : 000000000000000d x1 : 000000000000000c x0 : 0000000000000000
Call trace:
xas_split_alloc+0xf8/0x128
split_huge_page_to_list_to_order+0x1c4/0x780
truncate_inode_partial_folio+0xdc/0x160
truncate_inode_pages_range+0x1b4/0x4a8
truncate_pagecache_range+0x84/0xa0
xfs_flush_unmap_range+0x70/0x90 [xfs]
xfs_file_fallocate+0xfc/0x4d8 [xfs]
vfs_fallocate+0x124/0x2f0
ksys_fallocate+0x4c/0xa0
__arm64_sys_fallocate+0x24/0x38
invoke_syscall.constprop.0+0x7c/0xd8
do_el0_svc+0xb4/0xd0
el0_svc+0x44/0x1d8
el0t_64_sync_handler+0x134/0x150
el0t_64_sync+0x17c/0x180
Fix it by correcting the supported page cache orders, different sets for
DAX and other files. With it corrected, 512MB page cache becomes
disallowed on all non-DAX files on ARM64 system where the base page size
is 64KB. After this patch is applied, the test program fails with error
-EINVAL returned from __thp_vma_allowable_orders() and the madvise()
system call to collapse the page caches.
Link: https://lkml.kernel.org/r/20240715000423.316491-1-gshan@xxxxxxxxxx
Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache")
Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx>
Acked-by: Zi Yan <ziy@xxxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Barry Song <baohua@xxxxxxxxxx>
Cc: Don Dutile <ddutile@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [5.17+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/huge_mm.h | 12 +++++++++---
mm/huge_memory.c | 12 ++++++++++--
2 files changed, 19 insertions(+), 5 deletions(-)
--- a/include/linux/huge_mm.h~mm-huge_memory-avoid-pmd-size-page-cache-if-needed
+++ a/include/linux/huge_mm.h
@@ -72,14 +72,20 @@ extern struct kobj_attribute shmem_enabl
#define THP_ORDERS_ALL_ANON ((BIT(PMD_ORDER + 1) - 1) & ~(BIT(0) | BIT(1)))
/*
- * Mask of all large folio orders supported for file THP.
+ * Mask of all large folio orders supported for file THP. Folios in a DAX
+ * file is never split and the MAX_PAGECACHE_ORDER limit does not apply to
+ * it.
*/
-#define THP_ORDERS_ALL_FILE (BIT(PMD_ORDER) | BIT(PUD_ORDER))
+#define THP_ORDERS_ALL_FILE_DAX \
+ (BIT(PMD_ORDER) | BIT(PUD_ORDER))
+#define THP_ORDERS_ALL_FILE_DEFAULT \
+ ((BIT(MAX_PAGECACHE_ORDER + 1) - 1) & ~BIT(0))
/*
* Mask of all large folio orders supported for THP.
*/
-#define THP_ORDERS_ALL (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_FILE)
+#define THP_ORDERS_ALL \
+ (THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_FILE_DAX | THP_ORDERS_ALL_FILE_DEFAULT)
#define TVA_SMAPS (1 << 0) /* Will be used for procfs */
#define TVA_IN_PF (1 << 1) /* Page fault handler */
--- a/mm/huge_memory.c~mm-huge_memory-avoid-pmd-size-page-cache-if-needed
+++ a/mm/huge_memory.c
@@ -88,9 +88,17 @@ unsigned long __thp_vma_allowable_orders
bool smaps = tva_flags & TVA_SMAPS;
bool in_pf = tva_flags & TVA_IN_PF;
bool enforce_sysfs = tva_flags & TVA_ENFORCE_SYSFS;
+ unsigned long supported_orders;
+
/* Check the intersection of requested and supported orders. */
- orders &= vma_is_anonymous(vma) ?
- THP_ORDERS_ALL_ANON : THP_ORDERS_ALL_FILE;
+ if (vma_is_anonymous(vma))
+ supported_orders = THP_ORDERS_ALL_ANON;
+ else if (vma_is_dax(vma))
+ supported_orders = THP_ORDERS_ALL_FILE_DAX;
+ else
+ supported_orders = THP_ORDERS_ALL_FILE_DEFAULT;
+
+ orders &= supported_orders;
if (!orders)
return 0;
_
Patches currently in -mm which might be from gshan@xxxxxxxxxx are
mm-huge_memory-avoid-pmd-size-page-cache-if-needed.patch
