On Mon, Nov 13, 2017 at 02:46:25PM -0800, Dave Hansen wrote: > On 11/13/2017 02:20 PM, Dave Hansen wrote: > > On 11/09/2017 05:09 PM, Tycho Andersen wrote: > >> which I guess is from the additional flags in grow_dev_page() somewhere > >> down > >> the stack. Anyway... it seems this is a kernel allocation that's using > >> MIGRATE_MOVABLE, so perhaps we need some more fine tuned heuristic than > >> just > >> all MOVABLE allocations are un-mapped via xpfo, and all the others are > >> mapped. > >> > >> Do you have any ideas? > > > > It still has to do a kmap() or kmap_atomic() to be able to access it. I > > thought you hooked into that. Why isn't that path getting hit for these? > > Oh, this looks to be accessing data mapped by a buffer_head. It > (rudely) accesses data via: > > void set_bh_page(struct buffer_head *bh, > ... > bh->b_data = page_address(page) + offset;
We don't need to kmap in order to access MOVABLE allocations. kmap is only needed for HIGHMEM allocations. So there's nothing wrong with ext4 or set_bh_page().
