On Wed, Aug 22, 2012 at 03:36:48PM +0200, Hiroshi Doyu wrote: > Hi, > > KyongHo Cho <pullip.cho@xxxxxxxxxxx> wrote @ Wed, 22 Aug 2012 14:47:00 +0200: > > > vzalloc() call in __iommu_alloc_buffer() also causes BUG() in atomic context. > > Right. > > I've been thinking that kzalloc() may be enough here, since > vzalloc() was introduced to avoid allocation failure for big chunk of > memory, but I think that it's unlikely that the number of page array > can be so big. So I propose to drop vzalloc() here, and just simply to > use kzalloc only as below(*1). > > For example, > > 1920(H) x 1080(W) x 4(bytes) ~= 8MiB > > For 8 MiB buffer, > 8(MiB) * 1024 = 8192(KiB) > 8192(KiB) / 4(KiB/page) = 2048 pages > sizeof(struct page *) = 4 bytes > 2048(pages) * 4(bytes/page) = 8192(bytes) = 8(KiB) > 8(KiB) / 4(KiB/page) = 2 pages > > If the above estimation is right(I hope;)), the necessary pages are > _at most_ 2 pages. If the system gets into the situation to fail to > allocate 2 contiguous pages, that's real the problem. I guess that > that kind of fragmentation problem would be solved with page migration > or something, especially nowadays devices are getting larger memories. In atomic context, VM have no choice except relying on kswapd so high order allocation can fail easily when memory fragementation is high. -- Kind regards, Minchan Kim -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>