On (10/05/07 15:27), Christoph Lameter didst pronounce:
> On Thu, 10 May 2007, Mel Gorman wrote:
>
> > On (10/05/07 15:11), Christoph Lameter didst pronounce:
> > > On Thu, 10 May 2007, Mel Gorman wrote:
> > >
> > > > I see the gfpmask was 0x84020. That doesn't look like __GFP_WAIT was set,
> > > > right? Does that mean that SLUB is trying to allocate pages atomically? If so,
> > > > it would explain why this situation could still occur even though high-order
> > > > allocations that could sleep would succeed.
> > >
> > > SLUB is following the gfp mask of the caller like all well behaved slab
> > > allocators do. If the caller does not set __GFP_WAIT then the page
> > > allocator also cannot wait.
> >
> > Then SLUB should not use the higher orders for slab allocations that cannot
> > sleep during allocations. What could be done in the longer term is decide
> > how to tell kswapd to keep pages free at an order other than 0 when it is
> > known there are a large number of high-order long-lived allocations like this.
>
> I cannot predict how allocations on a slab will be performed. In order
> to avoid the higher order allocations in we would have to add a flag
> that tells SLUB at slab creation creation time that this cache will be
> used for atomic allocs and thus we can avoid configuring slabs in such a
> way that they use higher order allocs.
>
It is an option. I had the gfp flags passed in to kmem_cache_create() in
mind for determining this but SLUB creates slabs differently and different
flags could be passed into kmem_cache_alloc() of course.
> The other solution is not to use higher order allocations by dropping the
> antifrag patches in mm that allow SLUB to use higher order allocations.
> But then there would be no higher order allocations at all that would
> use the benefits of antifrag measures.
That would be an immediate solution.
Another alternative is that anti-frag used to also group high-order
allocations together and make it hard to fallback to those areas
for non-atomic allocations. It is currently backed out by the
patch dont-group-high-order-atomic-allocations.patch because
it was intended for rare high-order short-lived allocations
such as e1000 that are currently dealt with by MIGRATE_RESERVE
(bias-the-location-of-pages-freed-for-min_free_kbytes-in-the-same-max_order_nr_pages-blocks.patch)
. The high-order atomic groupings may help here because the high-order
allocations are long-lived and would claim contiguous areas.
The last alternative I think I mentioned already is to have the minimum
order kswapd reclaims as the same order SLUB uses instead of 0 so that
min_free_kbytes is kept at higher orders than current.
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
