Messages in this thread | | | Date | Fri, 27 Jan 2006 13:07:54 +0200 | From | Pekka Enberg <> | Subject | Re: [patch 0/9] Critical Mempools |
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Hi,
Pekka wrote: > > As as side note, we already have __GFP_NOFAIL. How is it different > > from GFP_CRITICAL and why aren't we improving that?
On 1/27/06, Paul Jackson <pj@sgi.com> wrote: > Don't these two flags invoke two different mechanisms. > __GFP_NOFAIL can sleep for HZ/50 then retry, rather than return failure. > __GFP_CRITICAL can steal from the emergency pool rather than fail. > > I would favor renaming at least the __GFP_CRITICAL to something > like __GFP_EMERGPOOL, to highlight the relevant distinction.
Yeah you're right. __GFP_NOFAIL guarantees to never fail but it doesn't guarantee to actually succeed either. I think the suggested semantics for __GFP_EMERGPOOL are that while it can fail, it tries to avoid that by dipping into page reserves. However, I do still think it's a bad idea to allow the slab allocator to steal whole pages for critical allocations because in low-memory condition, it should be fairly easy to exhaust the reserves and waste most of that memory at the same time.
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