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Message-Id: <20221024204830.1342169-3-peterx@redhat.com>
Date: Mon, 24 Oct 2022 16:48:30 -0400
From: Peter Xu <peterx@...hat.com>
To: linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc: Huang Ying <ying.huang@...el.com>, peterx@...hat.com,
Andrew Morton <akpm@...ux-foundation.org>,
HORIGUCHI NAOYA <naoya.horiguchi@....com>,
Miaohe Lin <linmiaohe@...wei.com>,
David Hildenbrand <david@...hat.com>,
Andrea Arcangeli <aarcange@...hat.com>
Subject: [PATCH RFC 2/2] mm: Use pte markers for swap errors
PTE markers are ideal mechanism for things like SWP_SWAPIN_ERROR. Using a
whole swap entry type for this purpose can be an overkill, especially if we
already have PTE markers. Define a new bit for swapin error and replace it
with pte markers. Then we can safely drop SWP_SWAPIN_ERROR and give one
device slot back to swap.
We used to have SWP_SWAPIN_ERROR taking the page pfn as part of the swap
entry, but it's never used. Neither do I see how it can be useful because
normally the swapin failure should not be caused by a bad page but bad swap
device. Drop it alongside.
Signed-off-by: Peter Xu <peterx@...hat.com>
---
include/linux/swap.h | 6 +-----
include/linux/swapops.h | 26 ++++++++++++++------------
mm/memory.c | 6 ++++--
mm/shmem.c | 2 +-
mm/swapfile.c | 2 +-
5 files changed, 21 insertions(+), 21 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 211aeca9bfa7..fec6647a289a 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -55,10 +55,6 @@ static inline int current_is_kswapd(void)
* actions on faults.
*/
-#define SWP_SWAPIN_ERROR_NUM 1
-#define SWP_SWAPIN_ERROR (MAX_SWAPFILES + SWP_HWPOISON_NUM + \
- SWP_MIGRATION_NUM + SWP_DEVICE_NUM + \
- SWP_PTE_MARKER_NUM)
/*
* PTE markers are used to persist information onto PTEs that otherwise
* should be a none pte. As its name "PTE" hints, it should only be
@@ -121,7 +117,7 @@ static inline int current_is_kswapd(void)
#define MAX_SWAPFILES \
((1 << MAX_SWAPFILES_SHIFT) - SWP_DEVICE_NUM - \
SWP_MIGRATION_NUM - SWP_HWPOISON_NUM - \
- SWP_PTE_MARKER_NUM - SWP_SWAPIN_ERROR_NUM)
+ SWP_PTE_MARKER_NUM)
/*
* Magic header for a swap area. The first part of the union is
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 41a6e7b23415..dd087b7287b0 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -162,16 +162,6 @@ static inline void *swp_to_radix_entry(swp_entry_t entry)
return xa_mk_value(entry.val);
}
-static inline swp_entry_t make_swapin_error_entry(struct page *page)
-{
- return swp_entry(SWP_SWAPIN_ERROR, page_to_pfn(page));
-}
-
-static inline int is_swapin_error_entry(swp_entry_t entry)
-{
- return swp_type(entry) == SWP_SWAPIN_ERROR;
-}
-
#if IS_ENABLED(CONFIG_DEVICE_PRIVATE)
static inline swp_entry_t make_readable_device_private_entry(pgoff_t offset)
{
@@ -409,8 +399,9 @@ static inline bool is_migration_entry_dirty(swp_entry_t entry)
typedef unsigned long pte_marker;
-#define PTE_MARKER_UFFD_WP BIT(0)
-#define PTE_MARKER_MASK (PTE_MARKER_UFFD_WP)
+#define PTE_MARKER_UFFD_WP BIT(0)
+#define PTE_MARKER_SWAP_ERROR BIT(1)
+#define PTE_MARKER_MASK (BIT(2) - 1)
static inline swp_entry_t make_pte_marker_entry(pte_marker marker)
{
@@ -437,6 +428,17 @@ static inline pte_t make_pte_marker(pte_marker marker)
return swp_entry_to_pte(make_pte_marker_entry(marker));
}
+static inline swp_entry_t make_swapin_error_entry(void)
+{
+ return make_pte_marker_entry(PTE_MARKER_SWAP_ERROR);
+}
+
+static inline int is_swapin_error_entry(swp_entry_t entry)
+{
+ return is_pte_marker_entry(entry) &&
+ (pte_marker_get(entry) & PTE_MARKER_SWAP_ERROR);
+}
+
/*
* This is a special version to check pte_none() just to cover the case when
* the pte is a pte marker. It existed because in many cases the pte marker
diff --git a/mm/memory.c b/mm/memory.c
index 71114f05a68c..cf602c3854c3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3705,6 +3705,10 @@ static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
if (WARN_ON_ONCE(!marker))
return VM_FAULT_SIGBUS;
+ /* Higher priority than uffd-wp when data corrupted */
+ if (marker & PTE_MARKER_SWAP_ERROR)
+ return VM_FAULT_SIGBUS;
+
if (pte_marker_entry_uffd_wp(entry))
return pte_marker_handle_uffd_wp(vmf);
@@ -3764,8 +3768,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
put_page(vmf->page);
} else if (is_hwpoison_entry(entry)) {
ret = VM_FAULT_HWPOISON;
- } else if (is_swapin_error_entry(entry)) {
- ret = VM_FAULT_SIGBUS;
} else if (is_pte_marker_entry(entry)) {
ret = handle_pte_marker(vmf);
} else {
diff --git a/mm/shmem.c b/mm/shmem.c
index c5f7a6668416..47dc595e98a3 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1682,7 +1682,7 @@ static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index,
swp_entry_t swapin_error;
void *old;
- swapin_error = make_swapin_error_entry(&folio->page);
+ swapin_error = make_swapin_error_entry();
old = xa_cmpxchg_irq(&mapping->i_pages, index,
swp_to_radix_entry(swap),
swp_to_radix_entry(swapin_error), 0);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5fc1237a9f21..13f2569a6719 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1781,7 +1781,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
pte_t pteval;
dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
- pteval = swp_entry_to_pte(make_swapin_error_entry(page));
+ pteval = swp_entry_to_pte(make_swapin_error_entry());
set_pte_at(vma->vm_mm, addr, pte, pteval);
swap_free(entry);
ret = 0;
--
2.37.3
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