On Wed, Jun 27, 2012 at 09:26:14AM +0100, Mel Gorman wrote:
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index b6c0727..5c6d9c6 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -2265,7 +2265,11 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
> > > if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) {
> > > if (gfp_mask & __GFP_MEMALLOC)
> > > alloc_flags |= ALLOC_NO_WATERMARKS;
> > > - else if (likely(!(gfp_mask & __GFP_NOMEMALLOC)) && !in_interrupt())
> > > + else if (in_serving_softirq() && (current->flags & PF_MEMALLOC))
> > > + alloc_flags |= ALLOC_NO_WATERMARKS;
> > > + else if (!in_interrupt() &&
> > > + ((current->flags & PF_MEMALLOC) ||
> > > + unlikely(test_thread_flag(TIF_MEMDIE))))
> > > alloc_flags |= ALLOC_NO_WATERMARKS;
> > > }
> >
> > You allocate in RX path with __GFP_MEMALLOC and your sk->sk_allocation has
> > also __GFP_MEMALLOC set. That means you should get ALLOC_NO_WATERMARKS in
> > alloc_flags.
>
> In the cases where they are annotated correctly, yes. It is recordeed if
> the page gets allocated from the PFMEMALLOC reserves. If the received
> packet is not SOCK_MEMALLOC and the page was allocated from PFMEMALLOC
> reserves it is then discarded and the packet must be retransmitted.
Let me try again:
- lets assume your allocation happens with alloc_page(), without
__GFP_MEMALLOC in GFP_FLAGS and with PF_MEMALLOC in current->flags. Now
you may get memory which you wouldn't receive otherwise (without
PF_MEMALLOC). Okay, understood. So you don't have to annotate each page
allocation in your receive path for instance as long as the process has the
flag set.
- lets assume your allocation happens with kmalloc() without __GFP_MEMALLOC
and current->flags has PF_MEMALLOC ORed and your SLAB pool is empty. This
forces SLAB to allocate more pages from the buddy allocator with it will
receive more likely (due to ->current->flags + PF_MEMALLOC) but SLAB will
drop this extra memory because the page has ->pf_memory (or something like
that) set and the GFP_FLAGS do not have __GFP_MEMALLOC set.
Is there something I missed?
Sebastian
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