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Date: Thu, 2 Dec 2010 16:16:51 -0800
From: Michel Lespinasse <walken@...gle.com>
To: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>,
Rik van Riel <riel@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Nick Piggin <npiggin@...nel.dk>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: linux-kernel@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5/6] mlock: do not hold mmap_sem for extended periods of time
__get_user_pages gets a new 'nonblocking' parameter to signal that the
caller is prepared to re-acquire mmap_sem and retry the operation if needed.
This is used to split off long operations if they are going to block on
a disk transfer, or when we detect contention on the mmap_sem.
Signed-off-by: Michel Lespinasse <walken@...gle.com>
---
mm/internal.h | 3 ++-
mm/memory.c | 27 ++++++++++++++++++++++-----
mm/mlock.c | 34 ++++++++++++++++++++--------------
mm/nommu.c | 6 ++++--
4 files changed, 48 insertions(+), 22 deletions(-)
diff --git a/mm/internal.h b/mm/internal.h
index dedb0af..bd4f581 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -243,7 +243,8 @@ static inline void mminit_validate_memmodel_limits(unsigned long *start_pfn,
int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, int len, unsigned int foll_flags,
- struct page **pages, struct vm_area_struct **vmas);
+ struct page **pages, struct vm_area_struct **vmas,
+ int *nonblocking);
#define ZONE_RECLAIM_NOSCAN -2
#define ZONE_RECLAIM_FULL -1
diff --git a/mm/memory.c b/mm/memory.c
index f3a9242..85e56dc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1366,7 +1366,8 @@ no_page_table:
int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, int nr_pages, unsigned int gup_flags,
- struct page **pages, struct vm_area_struct **vmas)
+ struct page **pages, struct vm_area_struct **vmas,
+ int *nonblocking)
{
int i;
unsigned long vm_flags;
@@ -1465,11 +1466,15 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
cond_resched();
while (!(page = follow_page(vma, start, foll_flags))) {
+ int fault_flags = 0;
int ret;
+ if (foll_flags & FOLL_WRITE)
+ fault_flags |= FAULT_FLAG_WRITE;
+ if (nonblocking)
+ fault_flags |= FAULT_FLAG_ALLOW_RETRY;
ret = handle_mm_fault(mm, vma, start,
- (foll_flags & FOLL_WRITE) ?
- FAULT_FLAG_WRITE : 0);
+ fault_flags);
if (ret & VM_FAULT_ERROR) {
if (ret & VM_FAULT_OOM)
@@ -1485,6 +1490,11 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
else
tsk->min_flt++;
+ if (ret & VM_FAULT_RETRY) {
+ *nonblocking = 0;
+ return i;
+ }
+
/*
* The VM_FAULT_WRITE bit tells us that
* do_wp_page has broken COW when necessary,
@@ -1516,6 +1526,11 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
i++;
start += PAGE_SIZE;
nr_pages--;
+ if (nonblocking && rwsem_is_contended(&mm->mmap_sem)) {
+ up_read(&mm->mmap_sem);
+ *nonblocking = 0;
+ return i;
+ }
} while (nr_pages && start < vma->vm_end);
} while (nr_pages);
return i;
@@ -1584,7 +1599,8 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
if (force)
flags |= FOLL_FORCE;
- return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas);
+ return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas,
+ NULL);
}
EXPORT_SYMBOL(get_user_pages);
@@ -1609,7 +1625,8 @@ struct page *get_dump_page(unsigned long addr)
struct page *page;
if (__get_user_pages(current, current->mm, addr, 1,
- FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma) < 1)
+ FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
+ NULL) < 1)
return NULL;
flush_cache_page(vma, addr, page_to_pfn(page));
return page;
diff --git a/mm/mlock.c b/mm/mlock.c
index 241a5d2..569ae6a 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -155,13 +155,13 @@ static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long add
* vma->vm_mm->mmap_sem must be held for at least read.
*/
static long __mlock_vma_pages_range(struct vm_area_struct *vma,
- unsigned long start, unsigned long end)
+ unsigned long start, unsigned long end,
+ int *nonblocking)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long addr = start;
int nr_pages = (end - start) / PAGE_SIZE;
int gup_flags;
- int ret;
VM_BUG_ON(start & ~PAGE_MASK);
VM_BUG_ON(end & ~PAGE_MASK);
@@ -187,9 +187,8 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
nr_pages--;
}
- ret = __get_user_pages(current, mm, addr, nr_pages, gup_flags,
- NULL, NULL);
- return max(ret, 0); /* 0 or negative error code */
+ return __get_user_pages(current, mm, addr, nr_pages, gup_flags,
+ NULL, NULL, nonblocking);
}
/*
@@ -233,7 +232,7 @@ long mlock_vma_pages_range(struct vm_area_struct *vma,
is_vm_hugetlb_page(vma) ||
vma == get_gate_vma(current))) {
- __mlock_vma_pages_range(vma, start, end);
+ __mlock_vma_pages_range(vma, start, end, NULL);
/* Hide errors from mmap() and other callers */
return 0;
@@ -429,21 +428,23 @@ static int do_mlock_pages(unsigned long start, size_t len)
struct mm_struct *mm = current->mm;
unsigned long end, nstart, nend;
struct vm_area_struct *vma = NULL;
+ int locked = 0;
int ret = 0;
VM_BUG_ON(start & ~PAGE_MASK);
VM_BUG_ON(len != PAGE_ALIGN(len));
end = start + len;
- down_read(&mm->mmap_sem);
for (nstart = start; nstart < end; nstart = nend) {
/*
* We want to fault in pages for [nstart; end) address range.
* Find first corresponding VMA.
*/
- if (!vma)
+ if (!locked) {
+ locked = 1;
+ down_read(&mm->mmap_sem);
vma = find_vma(mm, nstart);
- else
+ } else if (nstart >= vma->vm_end)
vma = vma->vm_next;
if (!vma || vma->vm_start >= end)
break;
@@ -456,16 +457,21 @@ static int do_mlock_pages(unsigned long start, size_t len)
continue;
if (nstart < vma->vm_start)
nstart = vma->vm_start;
/*
- * Now fault in a range of pages within the first VMA.
+ * Now fault in a range of pages. __mlock_vma_pages_range()
+ * double checks the vma flags, so that it won't mlock pages
+ * if the vma was already munlocked.
*/
- ret = __mlock_vma_pages_range(vma, nstart, nend);
- if (ret) {
+ ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
+ if (ret < 0) {
ret = __mlock_posix_error_return(ret);
break;
}
+ nend = nstart + ret * PAGE_SIZE;
+ ret = 0;
}
- up_read(&mm->mmap_sem);
+ if (locked)
+ up_read(&mm->mmap_sem);
return ret; /* 0 or negative error code */
}
diff --git a/mm/nommu.c b/mm/nommu.c
index 27a9ac5..c8b8a7e 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -127,7 +127,8 @@ unsigned int kobjsize(const void *objp)
int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, int nr_pages, unsigned int foll_flags,
- struct page **pages, struct vm_area_struct **vmas)
+ struct page **pages, struct vm_area_struct **vmas,
+ int *retry)
{
struct vm_area_struct *vma;
unsigned long vm_flags;
@@ -185,7 +186,8 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
if (force)
flags |= FOLL_FORCE;
- return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas);
+ return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas,
+ NULL);
}
EXPORT_SYMBOL(get_user_pages);
--
1.7.3.1
--
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