On Fri, 30 Jun 2017, Michal Hocko wrote: > On Fri 30-06-17 14:11:57, Mikulas Patocka wrote: > > > > > > On Fri, 30 Jun 2017, Michal Hocko wrote: > > > > > On Thu 29-06-17 22:25:09, Mikulas Patocka wrote: > > > > The __vmalloc function has a parameter gfp_mask with the allocation flags, > > > > however it doesn't fully respect the GFP_NOIO and GFP_NOFS flags. The > > > > pages are allocated with the specified gfp flags, but the pagetables are > > > > always allocated with GFP_KERNEL. This allocation can cause unexpected > > > > recursion into the filesystem or I/O subsystem. > > > > > > > > It is not practical to extend page table allocation routines with gfp > > > > flags because it would require modification of architecture-specific code > > > > in all architecturs. However, the process can temporarily request that all > > > > allocations are done with GFP_NOFS or GFP_NOIO with with the functions > > > > memalloc_nofs_save and memalloc_noio_save. > > > > > > > > This patch makes the vmalloc code use memalloc_nofs_save or > > > > memalloc_noio_save if the supplied gfp flags do not contain __GFP_FS or > > > > __GFP_IO. It fixes some possible deadlocks in drivers/mtd/ubi/io.c, > > > > fs/gfs2/, fs/btrfs/free-space-tree.c, fs/ubifs/, > > > > fs/nfs/blocklayout/extent_tree.c where __vmalloc is used with the GFP_NOFS > > > > flag. > > > > > > I strongly believe this is a step in the _wrong_ direction. Why? Because > > > > What do you think __vmalloc with GFP_NOIO should do? Print a warning? > > Silently ignore the GFP_NOIO flag? > > I think noio users are not that much different from nofs users. Simply > use the scope API at the place where the scope starts and document why > it is needed. vmalloc calls do not have to be any special then and they > do not even have to think about proper gfp flags and they can use > whatever is the default. > -- > Michal Hocko > SUSE Labs But you didn't answer the question - what should __vmalloc with GFP_NOIO (or GFP_NOFS) do? Silently drop the flag? Print a warning? Or respect the flag? Currently, it silently drops the GFP_NOIO or GFP_NOFS flag, but some programmers don't know it and use these flags. You can't blame those programmers for not knowing it. Mikulas -- 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>
