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SubjectRe: [PATCH] mm: fix NR_ISOLATED_[ANON|FILE] mismatch
On Thu, Sep 20, 2012 at 11:41:11AM -0400, Johannes Weiner wrote:
> On Thu, Sep 20, 2012 at 08:51:56AM +0900, Minchan Kim wrote:
> > From: Minchan Kim <minchan@kernel.org>
> > Date: Thu, 20 Sep 2012 08:39:52 +0900
> > Subject: [PATCH] mm: revert 0def08e3, mm/mempolicy.c: check return code of
> > check_range
> >
> > This patch reverts 0def08e3 because check_range can't fail in
> > migrate_to_node with considering current usecases.
> >
> > Quote from Johannes
> > "
> > I think it makes sense to revert. Not because of the semantics, but I
> > just don't see how check_range() could even fail for this callsite:
> >
> > 1. we pass mm->mmap->vm_start in there, so we should not fail due to
> > find_vma()
> >
> > 2. we pass MPOL_MF_DISCONTIG_OK, so the discontig checks do not apply
> > and so can not fail
> >
> > 3. we pass MPOL_MF_MOVE | MPOL_MF_MOVE_ALL, the page table loops will
> > continue until addr == end, so we never fail with -EIO
> > "
> >
> > And I add new VM_BUG_ON for checking migrate_to_node's future usecase
> > which might pass to MPOL_MF_STRICT.
> >
> > Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> > Cc: Mel Gorman <mgorman@suse.de>
> > Cc: Christoph Lameter <cl@linux.com>
> > Cc: David Rientjes <rientjes@google.com>
> > Cc: Vasiliy Kulikov <segooon@gmail.com>
> > Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> > mm/mempolicy.c | 9 +++++----
> > 1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index 3d64b36..9ec87bd 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -946,15 +946,16 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
> > nodemask_t nmask;
> > LIST_HEAD(pagelist);
> > int err = 0;
> > - struct vm_area_struct *vma;
> >
> > nodes_clear(nmask);
> > node_set(source, nmask);
> >
> > - vma = check_range(mm, mm->mmap->vm_start, mm->task_size, &nmask,
> > + /*
> > + * Collect migrate pages and it shoudn't be failed.
> > + */
> > + VM_BUG_ON(flags & MPOL_MF_STRICT);
>
> Adding a check and a comment is a good idea, but I'm not a big fan of
> checking for MPOL_MF_STRICT in particular because it's one of the
> invalid inputs, and so you need to extend this check when somebody
> extends the spectrum of invalid inputs. I would much prefer checking
> directly for !(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) instead, which
> would also make the possible inputs apparent without having to chase
> up the call chain to find out what is usually passed in.
>
> And how about
>
> /*
> * This does not "check" the range but isolates all pages that
> * need migration. Between passing in the full user address
> * space range and MPOL_MF_DISCONTIG_OK, this call can not fail.
> */
>
> ?

Good idea. Thanks Hannes,

From 13ae84083ac1f057eafbeae49efba862aa7a470e Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Fri, 21 Sep 2012 08:17:37 +0900
Subject: [PATCH] mm: enhance comment and bug check

This patch updates comment and bug check.
It can be fold into [1].

[1] mm-revert-0def08e3-mm-mempolicyc-check-return-code-of-check_range.patch

Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
mm/mempolicy.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 9ec87bd..0b78fb9 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -951,9 +951,11 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
node_set(source, nmask);

/*
- * Collect migrate pages and it shoudn't be failed.
+ * This does not "check" the range but isolates all pages that
+ * need migration. Between passing in the full user address
+ * space range and MPOL_MF_DISCONTIG_OK, this call can not fail.
*/
- VM_BUG_ON(flags & MPOL_MF_STRICT);
+ VM_BUG_ON(!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)));
check_range(mm, mm->mmap->vm_start, mm->task_size, &nmask,
flags | MPOL_MF_DISCONTIG_OK, &pagelist);

--
1.7.9.5
--
Kind regards,
Minchan Kim


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