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Subject[PATCH 1/1 v2] um/kernel/trap.c: Port OOM changes to handle_page_fault
Date
Commit d065bd810b6deb67d4897a14bfe21f8eb526ba99
(mm: retry page fault when blocking on disk transfer) and
commit 37b23e0525d393d48a7d59f870b3bc061a30ccdb
(x86,mm: make pagefault killable)

The above commits introduced changes into the x86 pagefault handler
for making the page fault handler retryable as well as killable.

These changes reduce the mmap_sem hold time, which is crucial
during OOM killer invocation.

Port these changes to um.

Signed-off-by: Kautuk Consul <consul.kautuk@gmail.com>
---
arch/um/kernel/trap.c | 24 +++++++++++++++++++-----
1 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index dafc947..76adb61 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -30,6 +30,8 @@ int handle_page_fault(unsigned long address, unsigned long ip,
pmd_t *pmd;
pte_t *pte;
int err = -EFAULT;
+ unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
+ (is_write ? FAULT_FLAG_WRITE : 0);

*code_out = SEGV_MAPERR;

@@ -40,6 +42,7 @@ int handle_page_fault(unsigned long address, unsigned long ip,
if (in_atomic())
goto out_nosemaphore;

+retry:
down_read(&mm->mmap_sem);
vma = find_vma(mm, address);
if (!vma)
@@ -65,7 +68,11 @@ good_area:
do {
int fault;

- fault = handle_mm_fault(mm, vma, address, is_write ? FAULT_FLAG_WRITE : 0);
+ fault = handle_mm_fault(mm, vma, address, flags);
+
+ if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ goto out_nosemaphore;
+
if (unlikely(fault & VM_FAULT_ERROR)) {
if (fault & VM_FAULT_OOM) {
goto out_of_memory;
@@ -75,10 +82,17 @@ good_area:
}
BUG();
}
- if (fault & VM_FAULT_MAJOR)
- current->maj_flt++;
- else
- current->min_flt++;
+ if (flags & FAULT_FLAG_ALLOW_RETRY) {
+ if (fault & VM_FAULT_MAJOR)
+ current->maj_flt++;
+ else
+ current->min_flt++;
+ if (fault & VM_FAULT_RETRY) {
+ flags &= ~FAULT_FLAG_ALLOW_RETRY;
+
+ goto retry;
+ }
+ }

pgd = pgd_offset(mm, address);
pud = pud_offset(pgd, address);
--
1.7.5.4


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