On (20/08/07 20:55), Nigel Cunningham didst pronounce: > Hi. > > On Monday 20 August 2007 18:59:36 Peter Zijlstra wrote: > > 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). > > I was just trying to make hibernation more reliable in sitations where > there's > low amounts of memory available. I guess the amount of memory that's reserved > for this has increased, because some users have been reporting issues that > hadn't appeared before. No problem. I'll work around it.
Where are these reports? I'm not familiar with how hibernation works but why does it need a large number of GFP_ATOMIC allocations? -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab - 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/
