On Mon, 2007-08-20 at 18:38 +1000, Nigel Cunningham wrote: > Hi. > > On Monday 20 August 2007 12:43:50 Peter Zijlstra wrote: > > On Mon, 2007-08-20 at 11:38 +1000, Nigel Cunningham wrote: > > > Hi all. > > > > > > In current git (and for a while now), an attempt to allocate memory with > > > GFP_ATOMIC will fail if we're below the low watermark level. The only way > to > > > access that memory that I can see (not that I've looked that hard) is to > have > > > PF_MEMALLOC set (ie from kswapd). I'm wondering if this behaviour is > correct. > > > Shouldn't GFP_ATOMIC allocations ignore watermarks too? How about > GFP_KERNEL? > > > > > > The following patch is a potential fix for GFP_ATOMIC. > > > > Sorry, no. > > > > GFP_ATOMIC must fail when below the watermark. GFP_KERNEL has __GFP_WAIT > > and hence can sleep and wait for reclaim so that should not be a problem > > (usually). > > > > GFP_ATOMIC may not access the reserves because the reserves are needed > > to get out of OOM deadlocks within the VM. Consider the fact that > > freeing memory needs memory - if there is no memory free, you cannot > > free memory and you're pretty much stuck. > > I guess, then, the question should be whether the watermark values are > appropriate. Do we need high order allocations watermarked if this is the > only purpose, particularly considering that whatever memory is allocated for > this purpose is essentially useless 99.9% of the time?
Could you perhaps explain what you're trying to do? No matter what we do, GFP_ATOMIC will fail eventually, there is only so much one can do without blocking. As for higher order allocations, until we have a full online defrag solution those too can fail at any moment (even with __GFP_WAIT). - 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/
