On Fri, Jan 10, 2014 at 05:12:27PM +0100, Oleg Nesterov wrote:
> The recent "[PATCH v6 tip/core/locking 3/8] Documentation/memory-barriers.txt:
> Prohibit speculative writes" from Paul says:
>
> No SMP architecture currently supporting Linux allows speculative
> writes,
>
> ...
>
>
On 01/09, Andrea Arcangeli wrote:
>
> >
> > But we probably need barrier() in between, we can't use ACCESS_ONCE().
>
> After get_page_unless_zero I don't think there's any need of
> barrier(). barrier() should have been implicit in __atomic_add_unless
> in fact it should be a full smp_mb() equivale
On Thu, Jan 09, 2014 at 03:04:47PM +0100, Oleg Nesterov wrote:
>
> > #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > page_head = page;
> > if (unlikely(PageTail(page))) {
> > put_page(page);
> >
> >
> > so I'm still not seeing how a tail page racing with a split ends up with
On Thu, Jan 09, 2014 at 08:43:50PM +0100, Oleg Nesterov wrote:
> get_page_unless_zero(), and recently it was documented that the kernel can
> rely on the control dependency to serialize LOAD + STORE.
Ok, that's cheap then.
>
> But we probably need barrier() in between, we can't use ACCESS_ONCE()
On 01/09, Andrea Arcangeli wrote:
>
> On Thu, Jan 09, 2014 at 03:04:47PM +0100, Oleg Nesterov wrote:
> > OK. Even if I am right, we can probably make another fix.
>
> I think the confusion here was to think this was related to the futex
> code, it isn't. This was just a generic theoretical problem
On Thu, Jan 09, 2014 at 03:04:47PM +0100, Oleg Nesterov wrote:
> OK. Even if I am right, we can probably make another fix.
I think the confusion here was to think this was related to the futex
code, it isn't. This was just a generic theoretical problem found
doing the futex cleanups but it's not r
On 01/09, Mel Gorman wrote:
>
> On Wed, Jan 08, 2014 at 08:04:43PM +0100, Oleg Nesterov wrote:
> >
> > Yes.
> >
> > But suppose that CPU B completes split_huge_page_to_list/munmap/etc
> > and frees this head page.
> >
>
> Where did the reference taken by get_huge_page_multiple go?
In __split_huge_
On Wed, Jan 08, 2014 at 08:04:43PM +0100, Oleg Nesterov wrote:
> On 01/08, Mel Gorman wrote:
> >
> > On Wed, Jan 08, 2014 at 05:13:38PM +0100, Oleg Nesterov wrote:
> > >
> > > Yes. But, for example, get_futex_key() does
> > >
> > > if (unlikely(PageTail(page))) {
> > > put_page(page);
>
On 01/08, Mel Gorman wrote:
>
> On Wed, Jan 08, 2014 at 05:13:38PM +0100, Oleg Nesterov wrote:
> >
> > Yes. But, for example, get_futex_key() does
> >
> > if (unlikely(PageTail(page))) {
> > put_page(page);
> >
> > why this put_page() can't race with _split? If nothing else, another
On Wed, Jan 08, 2014 at 05:13:38PM +0100, Oleg Nesterov wrote:
> On 01/08, Mel Gorman wrote:
> >
> > On Sat, Jan 04, 2014 at 05:43:47PM +0100, Oleg Nesterov wrote:
> > >
> > > get/put_page(thp_tail) paths do get_page_unless_zero(page_head) +
> > > compound_lock(). In theory this page_head can b
On 01/08, Mel Gorman wrote:
>
> On Sat, Jan 04, 2014 at 05:43:47PM +0100, Oleg Nesterov wrote:
> >
> > get/put_page(thp_tail) paths do get_page_unless_zero(page_head) +
> > compound_lock(). In theory this page_head can be already freed and
> > reallocated as alloc_pages(__GFP_COMP, smal
On Wed, Jan 08, 2014 at 11:54:00AM +, Mel Gorman wrote:
> On Sat, Jan 04, 2014 at 05:43:47PM +0100, Oleg Nesterov wrote:
> > On 01/03, Andrew Morton wrote:
> > >
> > > On Fri, 3 Jan 2014 20:55:47 +0100 Oleg Nesterov wrote:
> > >
> > > > get/put_page(thp_tail) paths do get_page_unless_zero(page
On Sat, Jan 04, 2014 at 05:43:47PM +0100, Oleg Nesterov wrote:
> On 01/03, Andrew Morton wrote:
> >
> > On Fri, 3 Jan 2014 20:55:47 +0100 Oleg Nesterov wrote:
> >
> > > get/put_page(thp_tail) paths do get_page_unless_zero(page_head) +
> > > compound_lock(). In theory this page_head can be already
On 01/03, Andrew Morton wrote:
>
> On Fri, 3 Jan 2014 20:55:47 +0100 Oleg Nesterov wrote:
>
> > get/put_page(thp_tail) paths do get_page_unless_zero(page_head) +
> > compound_lock(). In theory this page_head can be already freed and
> > reallocated as alloc_pages(__GFP_COMP, smaller_order). In thi
On Fri, 3 Jan 2014 20:55:47 +0100 Oleg Nesterov wrote:
> get/put_page(thp_tail) paths do get_page_unless_zero(page_head) +
> compound_lock(). In theory this page_head can be already freed and
> reallocated as alloc_pages(__GFP_COMP, smaller_order). In this case
> get_page_unless_zero() can succee
get/put_page(thp_tail) paths do get_page_unless_zero(page_head) +
compound_lock(). In theory this page_head can be already freed and
reallocated as alloc_pages(__GFP_COMP, smaller_order). In this case
get_page_unless_zero() can succeed right after set_page_refcounted(),
and compound_lock() can race
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