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authorMichel Lespinasse <walken@google.com>2011-01-13 15:46:10 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-01-13 17:32:35 -0800
commitfed067da46ad3b9acedaf794a5f05d0bc153280b (patch)
treeba2eadd8c3c2884d15a5a9373924b33b40bdca7e /mm/mlock.c
parent5ecfda041e4b4bd858d25bbf5a16c2a6c06d7272 (diff)
downloadlinux-linaro-stable-fed067da46ad3b9acedaf794a5f05d0bc153280b.tar.gz
mlock: only hold mmap_sem in shared mode when faulting in pages
Currently mlock() holds mmap_sem in exclusive mode while the pages get faulted in. In the case of a large mlock, this can potentially take a very long time, during which various commands such as 'ps auxw' will block. This makes sysadmins unhappy: real 14m36.232s user 0m0.003s sys 0m0.015s (output from 'time ps auxw' while a 20GB file was being mlocked without being previously preloaded into page cache) I propose that mlock() could release mmap_sem after the VM_LOCKED bits have been set in all appropriate VMAs. Then a second pass could be done to actually mlock the pages, in small batches, releasing mmap_sem when we block on disk access or when we detect some contention. This patch: Before this change, mlock() holds mmap_sem in exclusive mode while the pages get faulted in. In the case of a large mlock, this can potentially take a very long time. Various things will block while mmap_sem is held, including 'ps auxw'. This can make sysadmins angry. I propose that mlock() could release mmap_sem after the VM_LOCKED bits have been set in all appropriate VMAs. Then a second pass could be done to actually mlock the pages with mmap_sem held for reads only. We need to recheck the vma flags after we re-acquire mmap_sem, but this is easy. In the case where a vma has been munlocked before mlock completes, pages that were already marked as PageMlocked() are handled by the munlock() call, and mlock() is careful to not mark new page batches as PageMlocked() after the munlock() call has cleared the VM_LOCKED vma flags. So, the end result will be identical to what'd happen if munlock() had executed after the mlock() call. In a later change, I will allow the second pass to release mmap_sem when blocking on disk accesses or when it is otherwise contended, so that it won't be held for long periods of time even in shared mode. Signed-off-by: Michel Lespinasse <walken@google.com> Tested-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Nick Piggin <npiggin@kernel.dk> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mlock.c')
-rw-r--r--mm/mlock.c81
1 files changed, 64 insertions, 17 deletions
diff --git a/mm/mlock.c b/mm/mlock.c
index 4f318642fbbe..67b3dd8616dc 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -377,18 +377,10 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
int ret = 0;
int lock = newflags & VM_LOCKED;
- if (newflags == vma->vm_flags ||
- (vma->vm_flags & (VM_IO | VM_PFNMAP)))
+ if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
+ is_vm_hugetlb_page(vma) || vma == get_gate_vma(current))
goto out; /* don't set VM_LOCKED, don't count */
- if ((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
- is_vm_hugetlb_page(vma) ||
- vma == get_gate_vma(current)) {
- if (lock)
- make_pages_present(start, end);
- goto out; /* don't set VM_LOCKED, don't count */
- }
-
pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
*prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
vma->vm_file, pgoff, vma_policy(vma));
@@ -424,14 +416,10 @@ success:
* set VM_LOCKED, __mlock_vma_pages_range will bring it back.
*/
- if (lock) {
+ if (lock)
vma->vm_flags = newflags;
- ret = __mlock_vma_pages_range(vma, start, end);
- if (ret < 0)
- ret = __mlock_posix_error_return(ret);
- } else {
+ else
munlock_vma_pages_range(vma, start, end);
- }
out:
*prev = vma;
@@ -444,7 +432,8 @@ static int do_mlock(unsigned long start, size_t len, int on)
struct vm_area_struct * vma, * prev;
int error;
- len = PAGE_ALIGN(len);
+ VM_BUG_ON(start & ~PAGE_MASK);
+ VM_BUG_ON(len != PAGE_ALIGN(len));
end = start + len;
if (end < start)
return -EINVAL;
@@ -487,6 +476,58 @@ static int do_mlock(unsigned long start, size_t len, int on)
return error;
}
+static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors)
+{
+ struct mm_struct *mm = current->mm;
+ unsigned long end, nstart, nend;
+ struct vm_area_struct *vma = NULL;
+ 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)
+ vma = find_vma(mm, nstart);
+ else
+ vma = vma->vm_next;
+ if (!vma || vma->vm_start >= end)
+ break;
+ /*
+ * Set [nstart; nend) to intersection of desired address
+ * range with the first VMA. Also, skip undesirable VMA types.
+ */
+ nend = min(end, vma->vm_end);
+ if (vma->vm_flags & (VM_IO | VM_PFNMAP))
+ continue;
+ if (nstart < vma->vm_start)
+ nstart = vma->vm_start;
+ /*
+ * Now fault in a range of pages within the first VMA.
+ */
+ if (vma->vm_flags & VM_LOCKED) {
+ ret = __mlock_vma_pages_range(vma, nstart, nend);
+ if (ret < 0 && ignore_errors) {
+ ret = 0;
+ continue; /* continue at next VMA */
+ }
+ if (ret) {
+ ret = __mlock_posix_error_return(ret);
+ break;
+ }
+ } else
+ make_pages_present(nstart, nend);
+ }
+ up_read(&mm->mmap_sem);
+ return ret; /* 0 or negative error code */
+}
+
SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
{
unsigned long locked;
@@ -512,6 +553,8 @@ SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
error = do_mlock(start, len, 1);
up_write(&current->mm->mmap_sem);
+ if (!error)
+ error = do_mlock_pages(start, len, 0);
return error;
}
@@ -576,6 +619,10 @@ SYSCALL_DEFINE1(mlockall, int, flags)
capable(CAP_IPC_LOCK))
ret = do_mlockall(flags);
up_write(&current->mm->mmap_sem);
+ if (!ret && (flags & MCL_CURRENT)) {
+ /* Ignore errors */
+ do_mlock_pages(0, TASK_SIZE, 1);
+ }
out:
return ret;
}