On Thu, Apr 14, 2011 at 05:14:41PM -0400, Johannes Weiner wrote: > The vmap allocator is used to, among other things, allocate per-cpu > vmap blocks, where each vmap block is naturally aligned to its own > size. Obviously, leaving a guard page after each vmap area forbids > packing vmap blocks efficiently and can make the kernel run out of > possible vmap blocks long before overall vmap space is exhausted. > > The new interface to map a user-supplied page array into linear > vmalloc space (vm_map_ram) insists on allocating from a vmap block > (instead of falling back to a custom area) when the area size is below > a certain threshold. With heavy users of this interface (e.g. XFS) > and limited vmalloc space on 32-bit, vmap block exhaustion is a real > problem. > > Remove the guard page from the core vmap allocator. vmalloc and the > old vmap interface enforce a guard page on their own at a higher > level. > > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Nick Piggin <npiggin@xxxxxxxxx> > Cc: Dave Chinner <david@xxxxxxxxxxxxx> > Cc: Mel Gorman <mel@xxxxxxxxx> > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> If necessary, the guard page could be reintroduced as a debugging-only option (CONFIG_DEBUG_PAGEALLOC?). Otherwise it seems reasonable. Acked-by: Mel Gorman <mel@xxxxxxxxx> -- Mel Gorman SUSE Labs -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>