Messages in this thread | | | Date | Sun, 29 Jun 2008 20:23:05 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH trivial] block: GFP_ATOMIC is __GFP_HIGH |
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On Sun, Jun 29 2008, Eduard - Gabriel Munteanu wrote: > On Sun, 29 Jun 2008 07:16:49 +0100 (BST) > Hugh Dickins <hugh@veritas.com> wrote: > > > but it is not > > accidental that GFP_ATOMIC includes __GFP_HIGH - it's precisely when > > we're atomic that we need access to those extra reserves; and where > > we don't actually want them then we do say GFP_NOWAIT not GFP_ATOMIC. > > I would expect GFP_ATOMIC just prevents sleeping, while it _could_ fail > (in theory) unless it is allowed to touch the emergency pools. > > Actually, in many/most atomic contexts bail-out paths are possible for > allocation failures. And many/most of these atomic contexts have no > special reason to require emergency memory. Think about the usual > allocations enclosed within spinlocks.
I have to agree with Eduard here - GFP_ATOMIC means "don't block" primarily, whether it has a given priority or not is something you would have to look up. So it's more readable with the __GFP_HIGH manually added.
> > I expect the gfp flags will change in the future; but unless I missed > > somewhere, amongst all the places which specify GFP_ATOMIC throughout > > the kernel, this is the only one which ors in __GFP_HIGH too. I don't > > believe it expected access to extra extra reserves! So I thought we'd > > do best to remove the anomaly. > > Yes, it seems this is the only place where this occurs. > > Although I did not read all the code and resolved its implications, it > seems like it actually needs something like __GFP_NOFAIL (?) instead of > __GFP_HIGH. The slab itself is created with SLAB_PANIC.
It's not a big deal, it'll recover fine.
-- Jens Axboe
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