On Tue, Jul 26, 2011 at 08:40:59AM +0900, Minchan Kim wrote: > Hi Andi, > > On Tue, Jul 26, 2011 at 5:37 AM, Andi Kleen <ak@xxxxxxxxxxxxxxx> wrote: > >> The global dirty limits are put in proportion to the respective zone's > >> amount of dirtyable memory and the allocation denied when the limit of > >> that zone is reached. > >> > >> Before the allocation fails, the allocator slowpath has a stage before > >> compaction and reclaim, where the flusher threads are kicked and the > >> allocator ultimately has to wait for writeback if still none of the > >> zones has become eligible for allocation again in the meantime. > >> > > > > I don't really like this. It seems wrong to make memory > > placement depend on dirtyness. > > > > Just try to explain it to some system administrator or tuner: her > > head will explode and for good reasons. > > > > On the other hand I like doing round-robin in filemap by default > > (I think that is what your patch essentially does) > > We should have made this default long ago. It avoids most of the > > "IO fills up local node" problems people run into all the time. > > > > So I would rather just change the default in filemap allocation. It's not only a problem that exists solely on a node-level but also on a zone-level. Round-robin over the nodes does not fix the problem that a small zone can fill up with dirty pages before the global dirty limit kicks in. > Just out of curiosity. > Why do you want to consider only filemap allocation, not IO(ie, > filemap + sys_[read/write]) allocation? I guess Andi was referring to the page cache (mapping file offsets to pages), rather than mmaps (mapping virtual addresses to pages). mm/filemap.c::__page_cache_alloc() -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>