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Date: Wed, 1 Dec 2010 09:14:14 +0900 (JST)
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To: Michel Lespinasse <walken@...gle.com>
Cc: kosaki.motohiro@...fujitsu.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hugh.dickins@...cali.co.uk>,
Nick Piggin <npiggin@...nel.dk>, Rik van Riel <riel@...hat.com>
Subject: Re: [RFC] mlock: release mmap_sem every 256 faulted pages
Hi
Sorry fot the delay. I reviewed this one.
> Hi,
>
> I'd like to sollicit comments on this proposal:
>
> 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.
>
> 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, never holding mmap_sem
> for longer than it takes to process one single batch. We need to recheck
> the vma flags whenever we re-acquire mmap_sem, but this is not difficult.
>
> This is only an RFC rather than an actual submission, as I think this
> could / should be completed to handle more than the mlock() and
> mlockall() cases (there are many call sites to mlock_vma_pages_range()
> that should ideally be converted as well), and maybe use the fault retry
> mechanism to drop mmap_sem when blocking on disk access rather than
> using an arbitrary page batch size.
>
> Patch is against v2.6.36, but should apply to linus tree too.
>
> ------------------------------- 8< -----------------------------
>
> Let mlock / mlockall release mmap_sem after the vmas have been marked
> as VM_LOCKED. Then, mark the vmas as mlocked in small batches.
> For every batch, we need to grab mmap_sem in read mode, check that the
> vma has not been munlocked, and mlock the pages.
>
> 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.
>
> Signed-off-by: Michel Lespinasse <walken@...gle.com>
Looks good.
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
some nit.
> ---
> mm/mlock.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++------------
> 1 files changed, 63 insertions(+), 16 deletions(-)
>
> diff --git a/mm/mlock.c b/mm/mlock.c
> index b70919c..0aa4df5 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -373,17 +373,11 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
> int lock = newflags & VM_LOCKED;
>
> if (newflags == vma->vm_flags ||
> - (vma->vm_flags & (VM_IO | VM_PFNMAP)))
> + (vma->vm_flags & (VM_IO | VM_PFNMAP |
> + VM_DONTEXPAND | VM_RESERVED)) ||
> + 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));
> @@ -419,14 +413,10 @@ 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;
> @@ -439,7 +429,8 @@ 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));
good cleanup. but please separate this. I think this change is unrelated 256 batch concept.
> end = start + len;
> if (end < start)
> return -EINVAL;
> @@ -482,6 +473,58 @@ 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)
> +{
> + struct mm_struct *mm = current->mm;
> + unsigned long end, nstart, nend, nfault;
> + struct vm_area_struct *vma;
> + int error = 0;
> +
> + VM_BUG_ON(start & ~PAGE_MASK);
> + VM_BUG_ON(len != PAGE_ALIGN(len));
> + end = start + len;
> +
> + for (nstart = start; nstart < end; nstart = nend) {
> + down_read(&mm->mmap_sem);
> + nend = end;
> + vma = find_vma_intersection(mm, nstart, nend);
> + if (!vma)
> + goto up;
every exception check branch need comments.
> + if (vma->vm_end < nend)
> + nend = vma->vm_end;
> + if (vma->vm_flags & (VM_IO | VM_PFNMAP))
> + goto up;
vm_flags should be checked at first. because we don't need nend adjustment.
> + if (nstart < vma->vm_start)
> + nstart = vma->vm_start;
> +
> + /*
> + * Limit batch size to 256 pages in order to reduce
> + * mmap_sem hold time.
> + */
> + nfault = nstart + 256 * PAGE_SIZE;
We don't need nfault variable. maybe.
> +
> + /*
> + * Now fault in a batch of pages. We need to check the vma
> + * flags again, as we've not been holding mmap_sem.
> + */
> + if ((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
> + is_vm_hugetlb_page(vma) || vma == get_gate_vma(current)) {
> + if (nfault < nend)
> + nend = nfault;
> + make_pages_present(nstart, nend);
> + } else if (vma->vm_flags & VM_LOCKED) {
> + if (nfault < nend)
> + nend = nfault;
Both branch has the same "nfault < nend" check. We can unify it.
> + error = __mlock_vma_pages_range(vma, nstart, nend);
> + }
> + up:
> + up_read(&mm->mmap_sem);
> + if (error)
> + return __mlock_posix_error_return(error);
Now, __mlock_posix_error_return() can be moved into __mlock_vma_pages_range().
> + }
> + return 0;
> +}
> +
> SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
> {
> unsigned long locked;
> @@ -507,6 +550,8 @@ 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(¤t->mm->mmap_sem);
> + if (!error)
> + error = do_mlock_pages(start, len);
> return error;
> }
>
> @@ -571,6 +616,8 @@ SYSCALL_DEFINE1(mlockall, int, flags)
> capable(CAP_IPC_LOCK))
> ret = do_mlockall(flags);
> up_write(¤t->mm->mmap_sem);
> + if (!ret && (flags & MCL_CURRENT))
> + ret = do_mlock_pages(0, TASK_SIZE);
> out:
> return ret;
> }
So, I'm waiting your testcase.
below is for explanation code. but you can ignore this. I don't think
your patch doesn't work.
Thanks.
From e4253f161d9c17ba67cd9a445c8b8f556f87ad8c Mon Sep 17 00:00:00 2001
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Date: Sat, 25 Dec 2010 04:12:21 +0900
Subject: [PATCH] cleanup
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
---
mm/mlock.c | 67 ++++++++++++++++++++++++++++++++---------------------------
1 files changed, 36 insertions(+), 31 deletions(-)
diff --git a/mm/mlock.c b/mm/mlock.c
index 0aa4df5..e44b7ac 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -142,6 +142,18 @@ static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long add
!vma_stack_continue(vma->vm_prev, addr);
}
+/*
+ * convert get_user_pages() return value to posix mlock() error
+ */
+static int __mlock_posix_error_return(long retval)
+{
+ if (retval == -EFAULT)
+ retval = -ENOMEM;
+ else if (retval == -ENOMEM)
+ retval = -EAGAIN;
+ return retval;
+}
+
/**
* __mlock_vma_pages_range() - mlock a range of pages in the vma.
* @vma: target vma
@@ -236,19 +248,7 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
ret = 0;
}
- return ret; /* 0 or negative error code */
-}
-
-/*
- * convert get_user_pages() return value to posix mlock() error
- */
-static int __mlock_posix_error_return(long retval)
-{
- if (retval == -EFAULT)
- retval = -ENOMEM;
- else if (retval == -ENOMEM)
- retval = -EAGAIN;
- return retval;
+ return __mlock_posix_error_return(ret);
}
/**
@@ -476,53 +476,58 @@ static int do_mlock(unsigned long start, size_t len, int on)
static int do_mlock_pages(unsigned long start, size_t len)
{
struct mm_struct *mm = current->mm;
- unsigned long end, nstart, nend, nfault;
+ unsigned long end, nstart, nend;
struct vm_area_struct *vma;
int error = 0;
VM_BUG_ON(start & ~PAGE_MASK);
VM_BUG_ON(len != PAGE_ALIGN(len));
- end = start + len;
+ end = nend = start + len;
- for (nstart = start; nstart < end; nstart = nend) {
+ for (nstart = start; nstart < end; nstart = nend, nend = end) {
down_read(&mm->mmap_sem);
- nend = end;
vma = find_vma_intersection(mm, nstart, nend);
+
+ /* VMA gone. We don't need anything. */
if (!vma)
goto up;
- if (vma->vm_end < nend)
+
+ /* IO mapped area can't be populated. skip it. */
+ if (vma->vm_flags & (VM_IO | VM_PFNMAP)) {
nend = vma->vm_end;
- if (vma->vm_flags & (VM_IO | VM_PFNMAP))
goto up;
- if (nstart < vma->vm_start)
- nstart = vma->vm_start;
+ }
/*
* Limit batch size to 256 pages in order to reduce
* mmap_sem hold time.
*/
- nfault = nstart + 256 * PAGE_SIZE;
+ nend = nstart + 256 * PAGE_SIZE;
+ if (nstart < vma->vm_start)
+ nstart = vma->vm_start;
+ if (vma->vm_end < nend)
+ nend = vma->vm_end;
/*
* Now fault in a batch of pages. We need to check the vma
* flags again, as we've not been holding mmap_sem.
*/
if ((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
- is_vm_hugetlb_page(vma) || vma == get_gate_vma(current)) {
- if (nfault < nend)
- nend = nfault;
+ is_vm_hugetlb_page(vma) || vma == get_gate_vma(current))
+ /* The vma has special attributes. Don't use PG_mlocked. */
make_pages_present(nstart, nend);
- } else if (vma->vm_flags & VM_LOCKED) {
- if (nfault < nend)
- nend = nfault;
+ else if (vma->vm_flags & VM_LOCKED)
error = __mlock_vma_pages_range(vma, nstart, nend);
- }
+ else
+ /* VM_LOCKED has been lost. we can skip this vma. */
+ nend = vma->vm_end;
up:
up_read(&mm->mmap_sem);
if (error)
- return __mlock_posix_error_return(error);
+ break;
}
- return 0;
+
+ return error;
}
SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
--
1.6.5.2
--
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