On Sat, 25 Nov 2006, Linus Torvalds wrote: > On Fri, 24 Nov 2006, Hugh Dickins wrote: > > > > You need to add in something like the patch below (mutatis mutandis > > for whichever approach you end up taking): tmpfs uses highmem pages > > for its swap vector blocks, noting where on swap the data pages are, > > and allocates them with mapping_gfp_mask(inode->i_mapping); but we > > don't have any mechanism in place for reclaiming or migrating those. > > I think this really just points out that you should _not_ put MOVABLE into > the "mapping_gfp_mask()" at all. > > The mapping_gfp_mask() should really just contain the "constraints" on > the allocation, not the "how the allocation is used". So things like "I > need all my pages to be in the 32bit DMA'able region" is a constraint on > the allocator, as is something like "I need the allocation to be atomic". > > But MOVABLE is really not a constraint on the allocator, it's a guarantee > by the code _calling_ the allocator that it will then make sure that it > _uses_ the allocation in a way that means that it is movable. > > So it shouldn't be a property of the mapping itself, it should always be a > property of the code that actually does the allocation. > > Hmm?
Not anything I feel strongly about, but I don't see it that way. mapping_gfp_mask() seems to me nothing more than a pragmatic way of getting the appropriate gfp_mask down to page_cache_alloc(). alloc_inode() initializes it to whatever suits most filesystems (currently GFP_HIGHUSER), and those who differ adjust it (e.g. block_dev has good reason to avoid highmem so sets it to GFP_USER instead). It used to be the case that several filesystems lacked kmap() where needed, and those too would set GFP_USER: what you call a constraint seems to me equally a property of the surrounding code. If __GFP_MOVABLE is coming in, and most fs's are indeed allocating movable pages, then I don't see why MOVABLE shouldn't be in the mapping_gfp_mask. Specifying MOVABLE constrains both the caller's use of the pages, and the way they are allocated; as does HIGHMEM. And we shouldn't be guided by the way tmpfs (ab?)uses that gfp_mask for its metadata allocations as well as its page_cache_alloc()s: that's just a special case. Though the ramfs case is more telling (its pagecache pages being not at present movable). Hugh - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
