Messages in this thread | | | Date | Tue, 30 Sep 2008 10:53:41 +0900 | From | Yasunori Goto <> | Subject | Re: setup_per_zone_pages_min(): zone->lock vs. zone->lru_lock |
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> On Mon, 29 Sep 2008 23:20:05 +0200 > Gerald Schaefer <gerald.schaefer@de.ibm.com> wrote: > > > On Mon, 2008-09-29 at 18:36 +0100, Andy Whitcroft wrote: > > > The allocator protects it freelists using zone->lock (as we can see in > > > rmqueue_bulk), so anything which manipulates those should also be using > > > that lock. move_freepages() is scanning the cmap and picking up free > > > pages directly off the free lists, it is expecting those lists to be > > > stable; it would appear to need zone->lock. It does look like > > > setup_per_zone_pages_min() is holding the wrong thing at first look. > > > > I just noticed that the spin_lock in that function is much older than the > > call to setup_zone_migrate_reserve(), which then calls move_freepages(). > > So it seems that the zone->lru_lock there does (did?) have another purpose, > > maybe protecting zone->present_pages/pages_min/etc. > > > Maybe.
The zone->lru_lock() have been used before memory hotplug code was implemented. But I can't find any reason why it have been used.
> > > Looks like the need for a zone->lock (if any) was added later, but I'm not > > sure if makes sense to take both locks together, or if the lru_lock is still > > needed at all. > > > At first look, replacing zone->lru_lock with zone->lock is enough... > This function is an only one function which use zone->lru_lock in page_alloc.c > And zone_watermark_ok() which access zone->pages_min/low/high is not under any > locks. So, taking zone->lru_lock here doesn't seem to be necessary...
I agree.
Bye. -- Yasunori Goto
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