@@ -169,7 +169,7 @@ retry:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
+ flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
* have already released it in __lock_page_or_retry
@@ -145,7 +145,6 @@ retry:
*/
if (unlikely((fault & VM_FAULT_RETRY) &&
(flags & FAULT_FLAG_ALLOW_RETRY))) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
}
@@ -521,12 +521,7 @@ retry:
}
if (fault & VM_FAULT_RETRY) {
- /*
- * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk of
- * starvation.
- */
if (mm_flags & FAULT_FLAG_ALLOW_RETRY) {
- mm_flags &= ~FAULT_FLAG_ALLOW_RETRY;
mm_flags |= FAULT_FLAG_TRIED;
goto retry;
}
@@ -319,9 +319,6 @@ retry:
regs, addr);
}
if (fault & VM_FAULT_RETRY) {
- /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation. */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
}
@@ -102,7 +102,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
}
@@ -167,7 +167,6 @@ retry:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
@@ -162,9 +162,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation. */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/*
@@ -236,7 +236,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/*
@@ -178,7 +178,6 @@ good_area:
tsk->min_flt++;
}
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/*
@@ -246,7 +246,6 @@ good_area:
1, regs, addr);
}
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
@@ -157,9 +157,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation. */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/*
@@ -181,7 +181,6 @@ good_area:
else
tsk->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
@@ -328,14 +328,12 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
-
/*
* No need to up_read(&mm->mmap_sem) as we would
* have already released it in __lock_page_or_retry
* in mm/filemap.c.
*/
-
+ flags |= FAULT_FLAG_TRIED;
goto retry;
}
}
@@ -590,13 +590,7 @@ good_area:
* case.
*/
if (unlikely(fault & VM_FAULT_RETRY)) {
- /* We retry only once */
if (flags & FAULT_FLAG_ALLOW_RETRY) {
- /*
- * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation.
- */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
}
@@ -144,11 +144,6 @@ good_area:
1, regs, addr);
}
if (fault & VM_FAULT_RETRY) {
- /*
- * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation.
- */
- flags &= ~(FAULT_FLAG_ALLOW_RETRY);
flags |= FAULT_FLAG_TRIED;
/*
@@ -513,10 +513,7 @@ retry:
fault = VM_FAULT_PFAULT;
goto out_up;
}
- /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation. */
- flags &= ~(FAULT_FLAG_ALLOW_RETRY |
- FAULT_FLAG_RETRY_NOWAIT);
+ flags &= ~FAULT_FLAG_RETRY_NOWAIT;
flags |= FAULT_FLAG_TRIED;
down_read(&mm->mmap_sem);
goto retry;
@@ -481,7 +481,6 @@ good_area:
regs, address);
}
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/*
@@ -261,7 +261,6 @@ good_area:
1, regs, address);
}
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
@@ -449,7 +449,6 @@ good_area:
1, regs, address);
}
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
@@ -97,7 +97,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
@@ -259,9 +259,7 @@ retry:
else
tsk->min_flt++;
if (fault & VM_FAULT_RETRY) {
- /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation. */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
+ flags |= FAULT_FLAG_TRIED;
goto retry;
}
}
@@ -1479,8 +1479,6 @@ good_area:
*/
if (unlikely((fault & VM_FAULT_RETRY) &&
(flags & FAULT_FLAG_ALLOW_RETRY))) {
- /* Retry at most once */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
}
@@ -128,7 +128,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
@@ -59,9 +59,10 @@ static vm_fault_t ttm_bo_vm_fault_idle(s
/*
* If possible, avoid waiting for GPU with mmap_sem
- * held.
+ * held. We only do this if the fault allows retry and this
+ * is the first attempt.
*/
- if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
+ if (fault_flag_allow_retry_first(vmf->flags)) {
ret = VM_FAULT_RETRY;
if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
goto out_unlock;
@@ -135,7 +136,12 @@ vm_fault_t ttm_bo_vm_reserve(struct ttm_
* for the buffer to become unreserved.
*/
if (unlikely(!dma_resv_trylock(bo->base.resv))) {
- if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
+ /*
+ * If the fault allows retry and this is the first
+ * fault attempt, we try to release the mmap_sem
+ * before waiting
+ */
+ if (fault_flag_allow_retry_first(vmf->flags)) {
if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
ttm_bo_get(bo);
up_read(&vmf->vma->vm_mm->mmap_sem);
@@ -394,6 +394,25 @@ extern pgprot_t protection_map[16];
* @FAULT_FLAG_REMOTE: The fault is not for current task/mm.
* @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch.
* @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal signals.
+ *
+ * About @FAULT_FLAG_ALLOW_RETRY and @FAULT_FLAG_TRIED: we can specify
+ * whether we would allow page faults to retry by specifying these two
+ * fault flags correctly. Currently there can be three legal combinations:
+ *
+ * (a) ALLOW_RETRY and !TRIED: this means the page fault allows retry, and
+ * this is the first try
+ *
+ * (b) ALLOW_RETRY and TRIED: this means the page fault allows retry, and
+ * we've already tried at least once
+ *
+ * (c) !ALLOW_RETRY and !TRIED: this means the page fault does not allow retry
+ *
+ * The unlisted combination (!ALLOW_RETRY && TRIED) is illegal and should never
+ * be used. Note that page faults can be allowed to retry for multiple times,
+ * in which case we'll have an initial fault with flags (a) then later on
+ * continuous faults with flags (b). We should always try to detect pending
+ * signals before a retry to make sure the continuous page faults can still be
+ * interrupted if necessary.
*/
#define FAULT_FLAG_WRITE 0x01
#define FAULT_FLAG_MKWRITE 0x02
@@ -414,6 +433,24 @@ extern pgprot_t protection_map[16];
FAULT_FLAG_KILLABLE | \
FAULT_FLAG_INTERRUPTIBLE)
+/**
+ * fault_flag_allow_retry_first - check ALLOW_RETRY the first time
+ *
+ * This is mostly used for places where we want to try to avoid taking
+ * the mmap_sem for too long a time when waiting for another condition
+ * to change, in which case we can try to be polite to release the
+ * mmap_sem in the first round to avoid potential starvation of other
+ * processes that would also want the mmap_sem.
+ *
+ * Return: true if the page fault allows retry and this is the first
+ * attempt of the fault handling; false otherwise.
+ */
+static inline bool fault_flag_allow_retry_first(unsigned int flags)
+{
+ return (flags & FAULT_FLAG_ALLOW_RETRY) &&
+ (!(flags & FAULT_FLAG_TRIED));
+}
+
#define FAULT_FLAG_TRACE \
{ FAULT_FLAG_WRITE, "WRITE" }, \
{ FAULT_FLAG_MKWRITE, "MKWRITE" }, \
@@ -1386,7 +1386,7 @@ EXPORT_SYMBOL_GPL(__lock_page_killable);
int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
unsigned int flags)
{
- if (flags & FAULT_FLAG_ALLOW_RETRY) {
+ if (fault_flag_allow_retry_first(flags)) {
/*
* CAUTION! In this case, mmap_sem is not released
* even though return 0.
@@ -400,10 +400,10 @@ static inline struct file *maybe_unlock_
/*
* FAULT_FLAG_RETRY_NOWAIT means we don't want to wait on page locks or
* anything, so we only pin the file and drop the mmap_sem if only
- * FAULT_FLAG_ALLOW_RETRY is set.
+ * FAULT_FLAG_ALLOW_RETRY is set, while this is the first attempt.
*/
- if ((flags & (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT)) ==
- FAULT_FLAG_ALLOW_RETRY) {
+ if (fault_flag_allow_retry_first(flags) &&
+ !(flags & FAULT_FLAG_RETRY_NOWAIT)) {
fpin = get_file(vmf->vma->vm_file);
up_read(&vmf->vma->vm_mm->mmap_sem);
}