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Message-ID: <20230501175025.36233-3-surenb@google.com>
Date: Mon, 1 May 2023 10:50:25 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: akpm@...ux-foundation.org
Cc: willy@...radead.org, hannes@...xchg.org, mhocko@...e.com,
josef@...icpanda.com, jack@...e.cz, ldufour@...ux.ibm.com,
laurent.dufour@...ibm.com, michel@...pinasse.org,
liam.howlett@...cle.com, jglisse@...gle.com, vbabka@...e.cz,
minchan@...gle.com, dave@...olabs.net, punit.agrawal@...edance.com,
lstoakes@...il.com, hdanton@...a.com, apopple@...dia.com,
surenb@...gle.com, linux-mm@...ck.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-team@...roid.com
Subject: [PATCH 3/3] mm: implement folio wait under VMA lock
Follow the same pattern as mmap_lock when waiting for folio by dropping
VMA lock before the wait and retrying once folio is available.
Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
include/linux/pagemap.h | 14 ++++++++++----
mm/filemap.c | 43 ++++++++++++++++++++++-------------------
mm/memory.c | 13 +++++++++----
3 files changed, 42 insertions(+), 28 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index a56308a9d1a4..6c9493314c21 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -896,8 +896,8 @@ 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);
+bool __folio_lock_or_retry(struct folio *folio, struct vm_area_struct *vma,
+ unsigned int flags, bool *lock_dropped);
void unlock_page(struct page *page);
void folio_unlock(struct folio *folio);
@@ -1002,10 +1002,16 @@ static inline int folio_lock_killable(struct folio *folio)
* __folio_lock_or_retry().
*/
static inline bool folio_lock_or_retry(struct folio *folio,
- struct mm_struct *mm, unsigned int flags)
+ struct vm_area_struct *vma, unsigned int flags,
+ bool *lock_dropped)
{
might_sleep();
- return folio_trylock(folio) || __folio_lock_or_retry(folio, mm, flags);
+ if (folio_trylock(folio)) {
+ *lock_dropped = false;
+ return true;
+ }
+
+ return __folio_lock_or_retry(folio, vma, flags, lock_dropped);
}
/*
diff --git a/mm/filemap.c b/mm/filemap.c
index 84f39114d4de..9c0fa8578b2f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1701,37 +1701,35 @@ static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait)
/*
* Return values:
- * true - folio is locked; mmap_lock is still held.
+ * true - folio is locked.
* false - 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 flags had FAULT_FLAG_VMA_LOCK set, meaning the operation is performed
- * with VMA lock only, the VMA lock is still held.
+ *
+ * lock_dropped indicates whether mmap_lock/VMA lock got dropped.
+ * mmap_lock/VMA lock is dropped when function fails to lock the folio,
+ * unless flags had both FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT
+ * set, in which case mmap_lock/VMA lock is still held.
*
* If neither ALLOW_RETRY nor KILLABLE are set, will always return true
- * with the folio locked and the mmap_lock unperturbed.
+ * with the folio locked and the mmap_lock/VMA lock unperturbed.
*/
-bool __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
- unsigned int flags)
+bool __folio_lock_or_retry(struct folio *folio, struct vm_area_struct *vma,
+ unsigned int flags, bool *lock_dropped)
{
- /* Can't do this if not holding mmap_lock */
- if (flags & FAULT_FLAG_VMA_LOCK)
- return false;
-
if (fault_flag_allow_retry_first(flags)) {
- /*
- * CAUTION! In this case, mmap_lock is not released
- * even though return 0.
- */
- if (flags & FAULT_FLAG_RETRY_NOWAIT)
+ if (flags & FAULT_FLAG_RETRY_NOWAIT) {
+ *lock_dropped = false;
return false;
+ }
- mmap_read_unlock(mm);
+ if (flags & FAULT_FLAG_VMA_LOCK)
+ vma_end_read(vma);
+ else
+ mmap_read_unlock(vma->vm_mm);
if (flags & FAULT_FLAG_KILLABLE)
folio_wait_locked_killable(folio);
else
folio_wait_locked(folio);
+ *lock_dropped = true;
return false;
}
if (flags & FAULT_FLAG_KILLABLE) {
@@ -1739,13 +1737,18 @@ bool __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
ret = __folio_lock_killable(folio);
if (ret) {
- mmap_read_unlock(mm);
+ if (flags & FAULT_FLAG_VMA_LOCK)
+ vma_end_read(vma);
+ else
+ mmap_read_unlock(vma->vm_mm);
+ *lock_dropped = true;
return false;
}
} else {
__folio_lock(folio);
}
+ *lock_dropped = false;
return true;
}
diff --git a/mm/memory.c b/mm/memory.c
index 8222acf74fd3..e1cd39f00756 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;
+ bool lock_dropped;
/*
* We need a reference to lock the folio because we don't hold
@@ -3580,8 +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)) {
+ if (!folio_lock_or_retry(folio, vma, vmf->flags, &lock_dropped)) {
folio_put(folio);
+ if (lock_dropped && vmf->flags & FAULT_FLAG_VMA_LOCK)
+ return VM_FAULT_VMA_UNLOCKED | VM_FAULT_RETRY;
return VM_FAULT_RETRY;
}
mmu_notifier_range_init_owner(&range, MMU_NOTIFY_EXCLUSIVE, 0,
@@ -3704,7 +3707,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
bool exclusive = false;
swp_entry_t entry;
pte_t pte;
- int locked;
+ bool locked;
+ bool lock_dropped;
vm_fault_t ret = 0;
void *shadow = NULL;
@@ -3837,9 +3841,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
goto out_release;
}
- locked = folio_lock_or_retry(folio, vma->vm_mm, vmf->flags);
-
+ locked = folio_lock_or_retry(folio, vma, vmf->flags, &lock_dropped);
if (!locked) {
+ if (lock_dropped && vmf->flags & FAULT_FLAG_VMA_LOCK)
+ ret |= VM_FAULT_VMA_UNLOCKED;
ret |= VM_FAULT_RETRY;
goto out_release;
}
--
2.40.1.495.gc816e09b53d-goog
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