On Thu, 21 Oct 2010 15:03:32 -0500 (CDT) Christoph Lameter <cl@xxxxxxxxx> wrote: > On Thu, 21 Oct 2010, Andrew Morton wrote: > > > The patch doesn't patch direct reclaim, in do_try_to_free_pages(). How > > come? > > Direct reclaim does not run node specific shrink_slab. Direct reclaim does > a general pass after the individual zones have been shrunk. > > > OK, maybe this. Suppose we have a machine with 800M lowmem and 200M > > highmem. And suppose the lowmem region is stuffed full of clean > > icache/dcache. A __GFP_HIGHMEM allocation should put pressure on > > lowmem to get some of those pages back. What we don't want to do is to > > keep on reclaiming the highmem zone and allocating pages from there, > > because the machine would effectively end up with only 200M available > > for pagecache. > > Shrinker reclaim is not zone specific. It either occurs on a node or on > the system as a whole. A failure of HIGHMEM allocation in the direct > reclaim path will result in shrinkers being called with NO_NUMA_NODE and > therefore global reclaim will take place everywhere. > > Per node reclaim occurs from kswapd and covers all zones of that node. > > > Please convince us that your patch doesn't screw up zone balancing? > > There are no slab allocations in HIGHMEM or MOVABLE. Nothing to balance > there. > The patch changes balance_pgdat() to not shrink slab when inspecting the highmem zone. It will therefore change zone balancing behaviour on a humble 1G laptop, will it not? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>