Messages in this thread | | | Subject | Re: [PATCH]: Free pages from local pcp lists under tight memory conditions | From | Rohit Seth <> | Date | Wed, 23 Nov 2005 09:54:42 -0800 |
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On Tue, 2005-11-22 at 21:36 -0800, Andrew Morton wrote: > Rohit Seth <rohit.seth@intel.com> wrote: > > > > Andrew, Linus, > > > > [PATCH]: This patch free pages (pcp->batch from each list at a time) from > > local pcp lists when a higher order allocation request is not able to > > get serviced from global free_list. > > > > This should help fix some of the earlier failures seen with order 1 allocations. > > > > I will send separate patches for: > > > > 1- Reducing the remote cpus pcp > > 2- Clean up page_alloc.c for CONFIG_HOTPLUG_CPU to use this code appropiately > > > > +static int > > +reduce_cpu_pcp(void ) > > > This significantly duplicates the existing drain_local_pages().
Yes. The main change in this new function is I'm only freeing batch number of pages from each pcp rather than draining out all of them (even under a little memory pressure). IMO, we should be more opportunistic here in alloc_pages in moving pages back to global page pool list. Thoughts?
As said earlier, I will be cleaning up the existing drain_local_pages in next follow up patch.
> > > > > + if (order > 0) > > + while (reduce_cpu_pcp()) { > > + if (get_page_from_freelist(gfp_mask, order, zonelist, alloc_flags)) > > This forgot to assign to local variable `page'! It'll return NULL and will > leak memory. > My bad. Will fix it.
> The `while' loop worries me for some reason, so I wimped out and just tried > the remote drain once. > Even after direct reclaim it probably does make sense to see how minimally we can service a higher order request.
> > + goto got_pg; > > + } > > + /* FIXME: Add the support for reducing/draining the remote pcps. > > This is easy enough to do. >
The couple of options that I wanted to think little more were (before attempting to do this part):
1- Whether use the IPI to get the remote CPUs to free pages from pcp or do it lazily (using work_pending or such). As at this point in execution we can definitely afford to get scheduled out.
2- Do we drain the whole pcp on remote processors or again follow the stepped approach (but may be with a steeper slope).
> We need to verify that this patch actually does something useful. > > I'm working on this. Will let you know later today if I can come with some workload easily hitting this additional logic.
Thanks, -rohit
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