[PATCH v3 4/8] mm: replace folio_lock_or_retry with folio_lock_fault

Suren Baghdasaryan
2023-06-27T04:23:36Z

Change folio_lock_or_retry to accept vm_fault struct and return the
vm_fault_t directly. This will be used later to return additional
information about the state of the mmap_lock upon return from this
function.

Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
include/linux/pagemap.h | 13 ++++++-------
mm/filemap.c | 29 +++++++++++++++--------------
mm/memory.c | 14 ++++++--------
3 files changed, 27 insertions(+), 29 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index a56308a9d1a4..0bc206c6f62c 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -896,8 +896,7 @@ static inline bool wake_page_match(struct wait_page_queue *wait_page,

void __folio_lock(struct folio *folio);
int __folio_lock_killable(struct folio *folio);
-bool __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
- unsigned int flags);
+vm_fault_t __folio_lock_fault(struct folio *folio, struct vm_fault *vmf);
void unlock_page(struct page *page);
void folio_unlock(struct folio *folio);

@@ -995,17 +994,17 @@ static inline int folio_lock_killable(struct folio *folio)
}

/*
- * folio_lock_or_retry - Lock the folio, unless this would block and the
+ * folio_lock_fault - Lock the folio, unless this would block and the
* caller indicated that it can handle a retry.
*
* Return value and mmap_lock implications depend on flags; see
- * __folio_lock_or_retry().
+ * __folio_lock_fault().
*/
-static inline bool folio_lock_or_retry(struct folio *folio,
- struct mm_struct *mm, unsigned int flags)
+static inline vm_fault_t folio_lock_fault(struct folio *folio,
+ struct vm_fault *vmf)
{
might_sleep();
- return folio_trylock(folio) || __folio_lock_or_retry(folio, mm, flags);
+ return folio_trylock(folio) ? 0 : __folio_lock_fault(folio, vmf);
}

/*
diff --git a/mm/filemap.c b/mm/filemap.c
index 00f01d8ead47..87b335a93530 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1701,46 +1701,47 @@ static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait)

/*
* Return values:
- * true - folio is locked; mmap_lock is still held.
- * false - folio is not locked.
+ * 0 - folio is locked.
+ * VM_FAULT_RETRY - folio is not locked.
* mmap_lock has been released (mmap_read_unlock(), unless flags had both
* FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in
* which case mmap_lock is still held.
*
- * If neither ALLOW_RETRY nor KILLABLE are set, will always return true
+ * If neither ALLOW_RETRY nor KILLABLE are set, will always return 0
* with the folio locked and the mmap_lock unperturbed.
*/
-bool __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
- unsigned int flags)
+vm_fault_t __folio_lock_fault(struct folio *folio, struct vm_fault *vmf)
{
- if (fault_flag_allow_retry_first(flags)) {
+ struct mm_struct *mm = vmf->vma->vm_mm;
+
+ if (fault_flag_allow_retry_first(vmf->flags)) {
/*
* CAUTION! In this case, mmap_lock is not released
- * even though return 0.
+ * even though return VM_FAULT_RETRY.
*/
- if (flags & FAULT_FLAG_RETRY_NOWAIT)
- return false;
+ if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
+ return VM_FAULT_RETRY;

mmap_read_unlock(mm);
- if (flags & FAULT_FLAG_KILLABLE)
+ if (vmf->flags & FAULT_FLAG_KILLABLE)
folio_wait_locked_killable(folio);
else
folio_wait_locked(folio);
- return false;
+ return VM_FAULT_RETRY;
}
- if (flags & FAULT_FLAG_KILLABLE) {
+ if (vmf->flags & FAULT_FLAG_KILLABLE) {
bool ret;

ret = __folio_lock_killable(folio);
if (ret) {
mmap_read_unlock(mm);
- return false;
+ return VM_FAULT_RETRY;
}
} else {
__folio_lock(folio);
}

- return true;
+ return 0;
}

/**
diff --git a/mm/memory.c b/mm/memory.c
index 9011ad63c41b..3c2acafcd7b6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3568,6 +3568,7 @@ static vm_fault_t remove_device_exclusive_entry(struct vm_fault *vmf)
struct folio *folio = page_folio(vmf->page);
struct vm_area_struct *vma = vmf->vma;
struct mmu_notifier_range range;
+ vm_fault_t ret;

/*
* We need a reference to lock the folio because we don't hold
@@ -3580,9 +3581,10 @@ static vm_fault_t remove_device_exclusive_entry(struct vm_fault *vmf)
if (!folio_try_get(folio))
return 0;

- if (!folio_lock_or_retry(folio, vma->vm_mm, vmf->flags)) {
+ ret = folio_lock_fault(folio, vmf);
+ if (ret) {
folio_put(folio);
- return VM_FAULT_RETRY;
+ return ret;
}
mmu_notifier_range_init_owner(&range, MMU_NOTIFY_EXCLUSIVE, 0,
vma->vm_mm, vmf->address & PAGE_MASK,
@@ -3704,7 +3706,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
bool exclusive = false;
swp_entry_t entry;
pte_t pte;
- int locked;
vm_fault_t ret = 0;
void *shadow = NULL;

@@ -3825,12 +3826,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
goto out_release;
}

- locked = folio_lock_or_retry(folio, vma->vm_mm, vmf->flags);
-
- if (!locked) {
- ret |= VM_FAULT_RETRY;
+ ret |= folio_lock_fault(folio, vmf);
+ if (ret & VM_FAULT_RETRY)
goto out_release;
- }

if (swapcache) {
/*
--
2.41.0.178.g377b9f9a00-goog