The patch titled
Subject: mm: shmem: fallback to page size splice if large folio has poisoned pages
has been added to the -mm mm-unstable branch. Its filename is
mm-shmem-fallback-to-page-size-splice-if-large-folio-has-poisoned-pages.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shmem-fallback-to-page-size-splice-if-large-folio-has-poisoned-pages.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Subject: mm: shmem: fallback to page size splice if large folio has poisoned pages
Date: Sat, 26 Oct 2024 21:51:52 +0800
The tmpfs has already supported the PMD-sized large folios, and splice()
can not read any pages if the large folio has a poisoned page, which is
not good as Matthew pointed out in a previous email[1]:
"so if we have hwpoison set on one page in a folio, we now can't read
bytes from any page in the folio? That seems like we've made a bad
situation worse."
Thus add a fallback to the PAGE_SIZE splice() still allows reading normal
pages if the large folio has hwpoisoned pages.
[1] https://lore.kernel.org/all/Zw_d0EVAJkpNJEbA@xxxxxxxxxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/e3737fbd5366c4de4337bf5f2044817e77a5235b.1729915173.git.baolin.wang@xxxxxxxxxxxxxxxxx
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 39 +++++++++++++++++++++++++++++++--------
1 file changed, 31 insertions(+), 8 deletions(-)
--- a/mm/shmem.c~mm-shmem-fallback-to-page-size-splice-if-large-folio-has-poisoned-pages
+++ a/mm/shmem.c
@@ -3291,11 +3291,16 @@ static ssize_t shmem_file_splice_read(st
len = min_t(size_t, len, npages * PAGE_SIZE);
do {
+ bool fallback_page_splice = false;
+ struct page *page = NULL;
+ pgoff_t index;
+ size_t size;
+
if (*ppos >= i_size_read(inode))
break;
- error = shmem_get_folio(inode, *ppos / PAGE_SIZE, 0, &folio,
- SGP_READ);
+ index = *ppos >> PAGE_SHIFT;
+ error = shmem_get_folio(inode, index, 0, &folio, SGP_READ);
if (error) {
if (error == -EINVAL)
error = 0;
@@ -3304,12 +3309,15 @@ static ssize_t shmem_file_splice_read(st
if (folio) {
folio_unlock(folio);
- if (folio_test_hwpoison(folio) ||
- (folio_test_large(folio) &&
- folio_test_has_hwpoisoned(folio))) {
+ page = folio_file_page(folio, index);
+ if (PageHWPoison(page)) {
error = -EIO;
break;
}
+
+ if (folio_test_large(folio) &&
+ folio_test_has_hwpoisoned(folio))
+ fallback_page_splice = true;
}
/*
@@ -3323,7 +3331,18 @@ static ssize_t shmem_file_splice_read(st
isize = i_size_read(inode);
if (unlikely(*ppos >= isize))
break;
- part = min_t(loff_t, isize - *ppos, len);
+ /*
+ * Fallback to PAGE_SIZE splice if the large folio has hwpoisoned
+ * pages.
+ */
+ if (likely(!fallback_page_splice)) {
+ size = len;
+ } else {
+ size_t offset = *ppos & ~PAGE_MASK;
+
+ size = min_t(loff_t, PAGE_SIZE - offset, len);
+ }
+ part = min_t(loff_t, isize - *ppos, size);
if (folio) {
/*
@@ -3331,8 +3350,12 @@ static ssize_t shmem_file_splice_read(st
* virtual addresses, take care about potential aliasing
* before reading the page on the kernel side.
*/
- if (mapping_writably_mapped(mapping))
- flush_dcache_folio(folio);
+ if (mapping_writably_mapped(mapping)) {
+ if (likely(!fallback_page_splice))
+ flush_dcache_folio(folio);
+ else
+ flush_dcache_page(page);
+ }
folio_mark_accessed(folio);
/*
* Ok, we have the page, and it's up-to-date, so we can
_
Patches currently in -mm which might be from baolin.wang@xxxxxxxxxxxxxxxxx are
mm-shmem-fix-khugepaged-activation-policy-for-shmem.patch
mm-shmem-update-iocb-ki_pos-directly-to-simplify-tmpfs-read-logic.patch
mm-shmem-improve-the-tmpfs-large-folio-read-performance.patch
mm-shmem-fallback-to-page-size-splice-if-large-folio-has-poisoned-pages.patch
