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Message-ID: <aS_ycQQh5n1cVIRk@gourry-fedora-PF4VCD3F>
Date: Wed, 3 Dec 2025 03:18:57 -0500
From: Gregory Price <gourry@...rry.net>
To: Jayaraj Rajappan <jayarajpr@...il.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
lorenzo.stoakes@...cle.com
Subject: Re: Calls to do_swap_page() from handle_pte_fault() on a system
where swap is not configured
On Wed, Dec 03, 2025 at 01:11:24PM +0530, Jayaraj Rajappan wrote:
> Hi,
>
> On a system where swap is not configured, profiling using Linux "perf"
> tool shows that do_swap_page() gets called from handle_pte_fault().
> Kernel version is 5.14.0. HugePages are disabled on the system. Trying
> to understand what could cause do_swap_page() to be called when there
> is no swap configured on the system.
>
all do_swap_page() call means is that the PTE is valid (something is
there) but not present (the present-bit is not set, or whatever that
particular architecture considers is present is not met)
static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
{
...
if (!vmf->pte)
return do_pte_missing(vmf);
if (!pte_present(vmf->orig_pte))
return do_swap_page(vmf);
}
There are other non-swap swap-entries that are handled by the same code.
Transient migrations, device private, etc etc.
swap-entries are being renamed "softleaf" entries here shortly:
https://lore.kernel.org/linux-mm/cover.1762812360.git.lorenzo.stoakes@oracle.com/
So it means "a software-entry is present" which could be any of:
enum softleaf_type {
/* Fundamental types. */
SOFTLEAF_NONE,
SOFTLEAF_SWAP,
/* Migration types. */
SOFTLEAF_MIGRATION_READ,
SOFTLEAF_MIGRATION_READ_EXCLUSIVE,
SOFTLEAF_MIGRATION_WRITE,
/* Device types. */
SOFTLEAF_DEVICE_PRIVATE_READ,
SOFTLEAF_DEVICE_PRIVATE_WRITE,
SOFTLEAF_DEVICE_EXCLUSIVE,
/* H/W posion types. */
SOFTLEAF_HWPOISON,
/* Marker types. */
SOFTLEAF_MARKER,
};
-------
+Cc Lorenzo:
do_swap_page() is a stale name now probably?
I know there was a hold-off on changing actual swap code, but maybe
worth changing do_swap_page -> do_softleaf_page?
Not build or anything tested (sorry it's 3am insomnia time), basically just:
s/do_swap_page/do_softleaf_page
s/DO_SWAP_PAGE/DO_SOFTLEAF_PAGE
No clue what's up with the special sparc stuff.
~Gregory
-------
>From 92de7131f74b9300ea711ceae98bbe137cf0058f Mon Sep 17 00:00:00 2001
From: Gregory Price <gourry@...rry.net>
Date: Wed, 3 Dec 2025 03:12:44 -0500
Subject: [PATCH] mm: rename do_swap_page to do_softleaf_page
do_swap_page is a stale function name with introductio of softleaf.
Signed-off-by: Gregory Price <gourry@...rry.net>
---
Documentation/admin-guide/mm/ksm.rst | 2 +-
Documentation/gpu/rfc/gpusvm.rst | 2 +-
.../translations/zh_CN/admin-guide/mm/ksm.rst | 2 +-
.../translations/zh_TW/admin-guide/mm/ksm.rst | 2 +-
arch/sparc/include/asm/pgtable_64.h | 4 ++--
include/linux/ksm.h | 4 ++--
include/linux/pgtable.h | 10 +++++-----
mm/internal.h | 2 +-
mm/khugepaged.c | 6 +++---
mm/ksm.c | 2 +-
mm/memory-failure.c | 2 +-
mm/memory.c | 10 +++++-----
mm/page_io.c | 2 +-
mm/rmap.c | 4 ++--
mm/shmem.c | 2 +-
mm/swapfile.c | 6 +++---
mm/zswap.c | 4 ++--
17 files changed, 33 insertions(+), 33 deletions(-)
diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index ad8e7a41f3b5..4c660dbc908e 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -286,7 +286,7 @@ cow_ksm
ksm_swpin_copy
is incremented every time a KSM page is copied when swapping in
- note that KSM page might be copied when swapping in because do_swap_page()
+ note that KSM page might be copied when swapping in because do_softleaf_page()
cannot do all the locking needed to reconstitute a cross-anon_vma KSM page.
Advisor
diff --git a/Documentation/gpu/rfc/gpusvm.rst b/Documentation/gpu/rfc/gpusvm.rst
index 469db1372f16..3a444bf2768b 100644
--- a/Documentation/gpu/rfc/gpusvm.rst
+++ b/Documentation/gpu/rfc/gpusvm.rst
@@ -14,7 +14,7 @@ Agreed upon design principles
this path. These are not required and generally a bad idea to
invent driver defined locks to seal core MM races.
* An example of a driver-specific lock causing issues occurred before
- fixing do_swap_page to lock the faulting page. A driver-exclusive lock
+ fixing do_softleaf_page to lock the faulting page. A driver-exclusive lock
in migrate_to_ram produced a stable livelock if enough threads read
the faulting page.
* Partial migration is supported (i.e., a subset of pages attempting to
diff --git a/Documentation/translations/zh_CN/admin-guide/mm/ksm.rst b/Documentation/translations/zh_CN/admin-guide/mm/ksm.rst
index 0029c4fd2201..269cb94362ce 100644
--- a/Documentation/translations/zh_CN/admin-guide/mm/ksm.rst
+++ b/Documentation/translations/zh_CN/admin-guide/mm/ksm.rst
@@ -191,7 +191,7 @@ cow_ksm
ksm_swpin_copy
在换入时，每次KSM页被复制时都会被递增。请注意，KSM页在换入时可能会被复
- 制，因为do_swap_page()不能做所有的锁，而需要重组一个跨anon_vma的KSM页。
+ 制，因为do_softleaf_page()不能做所有的锁，而需要重组一个跨anon_vma的KSM页。
--
Izik Eidus,
diff --git a/Documentation/translations/zh_TW/admin-guide/mm/ksm.rst b/Documentation/translations/zh_TW/admin-guide/mm/ksm.rst
index 1b4944b3cf61..afea57754c41 100644
--- a/Documentation/translations/zh_TW/admin-guide/mm/ksm.rst
+++ b/Documentation/translations/zh_TW/admin-guide/mm/ksm.rst
@@ -191,7 +191,7 @@ cow_ksm
ksm_swpin_copy
在換入時，每次KSM頁被複制時都會被遞增。請注意，KSM頁在換入時可能會被複
- 制，因爲do_swap_page()不能做所有的鎖，而需要重組一個跨anon_vma的KSM頁。
+ 制，因爲do_softleaf_page()不能做所有的鎖，而需要重組一個跨anon_vma的KSM頁。
--
Izik Eidus,
diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
index 615f460c50af..7fee128daf03 100644
--- a/arch/sparc/include/asm/pgtable_64.h
+++ b/arch/sparc/include/asm/pgtable_64.h
@@ -1054,8 +1054,8 @@ void adi_restore_tags(struct mm_struct *mm, struct vm_area_struct *vma,
int adi_save_tags(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long addr, pte_t oldpte);
-#define __HAVE_ARCH_DO_SWAP_PAGE
-static inline void arch_do_swap_page(struct mm_struct *mm,
+#define __HAVE_ARCH_DO_SOFTLEAF_PAGE
+static inline void arch_do_softleaf_page(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long addr,
pte_t pte, pte_t oldpte)
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index c982694c987b..a024ca1bae3a 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -81,10 +81,10 @@ static inline void ksm_exit(struct mm_struct *mm)
}
/*
- * When do_swap_page() first faults in from swap what used to be a KSM page,
+ * When do_softleaf_page() first faults in from swap what used to be a KSM page,
* no problem, it will be assigned to this vma's anon_vma; but thereafter,
* it might be faulted into a different anon_vma (or perhaps to a different
- * offset in the same anon_vma). do_swap_page() cannot do all the locking
+ * offset in the same anon_vma). do_softleaf_page() cannot do all the locking
* needed to reconstitute a cross-anon_vma KSM page: for now it has to make
* a copy, and leave remerging the pages to a later pass of ksmd.
*
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index b13b6f42be3c..21262969b6b3 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1142,8 +1142,8 @@ static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b)
}
#endif
-#ifndef __HAVE_ARCH_DO_SWAP_PAGE
-static inline void arch_do_swap_page_nr(struct mm_struct *mm,
+#ifndef __HAVE_ARCH_DO_SOFTLEAF_PAGE
+static inline void arch_do_softleaf_page_nr(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long addr,
pte_t pte, pte_t oldpte,
@@ -1157,17 +1157,17 @@ static inline void arch_do_swap_page_nr(struct mm_struct *mm,
* page is being swapped out, this metadata must be saved so it can be
* restored when the page is swapped back in. SPARC M7 and newer
* processors support an ADI (Application Data Integrity) tag for the
- * page as metadata for the page. arch_do_swap_page() can restore this
+ * page as metadata for the page. arch_do_softleaf_page() can restore this
* metadata when a page is swapped back in.
*/
-static inline void arch_do_swap_page_nr(struct mm_struct *mm,
+static inline void arch_do_softleaf_page_nr(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long addr,
pte_t pte, pte_t oldpte,
int nr)
{
for (int i = 0; i < nr; i++) {
- arch_do_swap_page(vma->vm_mm, vma, addr + i * PAGE_SIZE,
+ arch_do_softleaf_page(vma->vm_mm, vma, addr + i * PAGE_SIZE,
pte_advance_pfn(pte, i),
pte_advance_pfn(oldpte, i));
}
diff --git a/mm/internal.h b/mm/internal.h
index 04c307ee33ae..7019db4f6dd6 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -436,7 +436,7 @@ static inline vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
return ret;
}
-vm_fault_t do_swap_page(struct vm_fault *vmf);
+vm_fault_t do_softleaf_page(struct vm_fault *vmf);
void folio_rotate_reclaimable(struct folio *folio);
bool __folio_end_writeback(struct folio *folio);
void deactivate_file_folio(struct folio *folio);
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 89c33ef7aac3..a6e09e94834c 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1007,7 +1007,7 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
if (!pte++) {
/*
* Here the ptl is only used to check pte_same() in
- * do_swap_page(), so readonly version is enough.
+ * do_softleaf_page(), so readonly version is enough.
*/
pte = pte_offset_map_ro_nolock(mm, pmd, addr, &ptl);
if (!pte) {
@@ -1024,12 +1024,12 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
vmf.pte = pte;
vmf.ptl = ptl;
- ret = do_swap_page(&vmf);
+ ret = do_softleaf_page(&vmf);
/* Which unmaps pte (after perhaps re-checking the entry) */
pte = NULL;
/*
- * do_swap_page returns VM_FAULT_RETRY with released mmap_lock.
+ * do_softleaf_page returns VM_FAULT_RETRY with released mmap_lock.
* Note we treat VM_FAULT_RETRY as VM_FAULT_ERROR here because
* we do not retry here and swap entry will remain in pagetable
* resulting in later failure.
diff --git a/mm/ksm.c b/mm/ksm.c
index cfc182255c7b..002140f01bf5 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3124,7 +3124,7 @@ struct folio *ksm_might_need_to_copy(struct folio *folio,
if (PageHWPoison(page))
return ERR_PTR(-EHWPOISON);
if (!folio_test_uptodate(folio))
- return folio; /* let do_swap_page report the error */
+ return folio; /* let do_softleaf_page report the error */
new_folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, addr);
if (new_folio &&
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index fbc5a01260c8..07e3a17af119 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1104,7 +1104,7 @@ static int me_pagecache_dirty(struct page_state *ps, struct page *p)
* - but keep in the swap cache, so that when we return to it on
* a later page fault, we know the application is accessing
* corrupted data and shall be killed (we installed simple
- * interception code in do_swap_page to catch it).
+ * interception code in do_softleaf_page to catch it).
*
* Clean swap cache pages can be directly isolated. A later page fault will
* bring in the known good data from disk.
diff --git a/mm/memory.c b/mm/memory.c
index 6675e87eb7dd..6d31eda830a5 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3371,7 +3371,7 @@ int apply_to_existing_page_range(struct mm_struct *mm, unsigned long addr,
* handle_pte_fault chooses page fault handler according to an entry which was
* read non-atomically. Before making any commitment, on those architectures
* or configurations (e.g. i386 with PAE) which might give a mix of unmatched
- * parts, do_swap_page must check under lock before unmapping the pte and
+ * parts, do_softleaf_page must check under lock before unmapping the pte and
* proceeding (but do_wp_page is only called after already making such a check;
* and do_anonymous_page can safely check later on).
*/
@@ -4569,7 +4569,7 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf)
goto fallback;
/*
- * For do_swap_page, find the highest order where the aligned range is
+ * For do_softleaf_page, find the highest order where the aligned range is
* completely swap entries with contiguous swap offsets.
*/
order = highest_order(orders);
@@ -4618,7 +4618,7 @@ static DECLARE_WAIT_QUEUE_HEAD(swapcache_wq);
* We return with the mmap_lock locked or unlocked in the same cases
* as does filemap_fault().
*/
-vm_fault_t do_swap_page(struct vm_fault *vmf)
+vm_fault_t do_softleaf_page(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
struct folio *swapcache, *folio = NULL;
@@ -5008,7 +5008,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
VM_BUG_ON(!folio_test_anon(folio) ||
(pte_write(pte) && !PageAnonExclusive(page)));
set_ptes(vma->vm_mm, address, ptep, pte, nr_pages);
- arch_do_swap_page_nr(vma->vm_mm, vma, address,
+ arch_do_softleaf_page_nr(vma->vm_mm, vma, address,
pte, pte, nr_pages);
folio_unlock(folio);
@@ -6234,7 +6234,7 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
return do_pte_missing(vmf);
if (!pte_present(vmf->orig_pte))
- return do_swap_page(vmf);
+ return do_softleaf_page(vmf);
if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma))
return do_numa_page(vmf);
diff --git a/mm/page_io.c b/mm/page_io.c
index 3c342db77ce3..3bcc8487b600 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -514,7 +514,7 @@ static bool swap_read_folio_zeromap(struct folio *folio)
/*
* Swapping in a large folio that is partially in the zeromap is not
* currently handled. Return true without marking the folio uptodate so
- * that an IO error is emitted (e.g. do_swap_page() will sigbus).
+ * that an IO error is emitted (e.g. do_softleaf_page() will sigbus).
*/
if (WARN_ON_ONCE(swap_zeromap_batch(folio->swap, nr_pages,
&is_zeromap) != nr_pages))
diff --git a/mm/rmap.c b/mm/rmap.c
index f955f02d570e..21c3a40ee824 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2535,7 +2535,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
/*
* Store the pfn of the page in a special migration
- * pte. do_swap_page() will wait until the migration
+ * pte. do_softleaf_page() will wait until the migration
* pte is removed and then restart fault handling.
*/
if (writable)
@@ -2755,7 +2755,7 @@ struct page *make_device_exclusive(struct mm_struct *mm, unsigned long addr,
/*
* Store the pfn of the page in a special device-exclusive PFN swap PTE.
- * do_swap_page() will trigger the conversion back while holding the
+ * do_softleaf_page() will trigger the conversion back while holding the
* folio lock.
*/
entry = make_device_exclusive_entry(page_to_pfn(page));
diff --git a/mm/shmem.c b/mm/shmem.c
index ad18172ff831..7fa65a8501b4 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2092,7 +2092,7 @@ static struct folio *shmem_swap_alloc_folio(struct inode *inode,
* we may need to copy to a suitable page before moving to filecache.
*
* In a future release, this may well be extended to respect cpuset and
- * NUMA mempolicy, and applied also to anonymous pages in do_swap_page();
+ * NUMA mempolicy, and applied also to anonymous pages in do_softleaf_page();
* but for now it is a simple matter of zone.
*/
static bool shmem_should_replace_folio(struct folio *folio, gfp_t gfp)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index d12332423a06..40039586f56e 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1568,7 +1568,7 @@ static unsigned char swap_entry_put_locked(struct swap_info_struct *si,
* example, the following situation is possible.
*
* CPU1 CPU2
- * do_swap_page()
+ * do_softleaf_page()
* ... swapoff+swapon
* __read_swap_cache_async()
* swapcache_prepare()
@@ -1578,7 +1578,7 @@ static unsigned char swap_entry_put_locked(struct swap_info_struct *si,
*
* In __swap_duplicate(), the swap_map need to be checked before
* changing partly because the specified swap entry may be for another
- * swap device which has been swapoff. And in do_swap_page(), after
+ * swap device which has been swapoff. And in do_softleaf_page(), after
* the page is read from the swap device, the PTE is verified not
* changed with the page table locked to check whether the swap device
* has been swapoff or swapoff+swapon.
@@ -2201,7 +2201,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
rmap_t rmap_flags = RMAP_NONE;
/*
- * See do_swap_page(): writeback would be problematic.
+ * See do_softleaf_page(): writeback would be problematic.
* However, we do a folio_wait_writeback() just before this
* call and have the folio locked.
*/
diff --git a/mm/zswap.c b/mm/zswap.c
index 5d0f8b13a958..db85ad97ccdb 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1586,13 +1586,13 @@ bool zswap_store(struct folio *folio)
*
* -EIO: if the swapped out content was in zswap, but could not be loaded
* into the page due to a decompression failure. The folio is unlocked, but
- * NOT marked up-to-date, so that an IO error is emitted (e.g. do_swap_page()
+ * NOT marked up-to-date, so that an IO error is emitted (e.g. do_softleaf_page()
* will SIGBUS).
*
* -EINVAL: if the swapped out content was in zswap, but the page belongs
* to a large folio, which is not supported by zswap. The folio is unlocked,
* but NOT marked up-to-date, so that an IO error is emitted (e.g.
- * do_swap_page() will SIGBUS).
+ * do_softleaf_page() will SIGBUS).
*
* -ENOENT: if the swapped out content was not in zswap. The folio remains
* locked on return.
--
2.52.0
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