On Thu 19-03-15 14:55:58, Michal Hocko wrote: > On Thu 19-03-15 08:38:35, Neil Brown wrote: > [...] > > Nearly half the places in the kernel which call mapping_gfp_mask() remove the > > __GFP_FS bit. > > > > That suggests to me that it might make sense to have > > mapping_gfp_mask_fs() > > and > > mapping_gfp_mask_nofs() > > > > and let the presence of __GFP_FS (and __GFP_IO) be determined by the > > call-site rather than the filesystem. > > Sounds reasonable to me but filesystems tend to use this in a very > different ways. > - xfs drops GFP_FS in xfs_setup_inode so all page cache allocations are > NOFS. > - reiserfs drops GFP_FS only before calling read_mapping_page in > reiserfs_get_page and never restores the original mask. > - btrfs doesn't seem to rely on mapping_gfp_mask for anything other than > btree_inode (unless it gets inherrited in a way I haven't noticed). > - ext* doesn't seem to rely on the mapping gfp mask at all. > > So it is not clear to me how we should change that into callsites. But I > guess we can change at least the page fault path like the following. I > like it much more than the previous way which is too hackish. But this is racy instead... And I do not think we can make it raceless so scratch this and get back to the original approach. [...] > + /* > + * Some filesystems always drop __GFP_FS to prevent from reclaim > + * recursion back to FS code. This is not the case here because > + * we are at the top of the call chain. Add GFP_FS flags to prevent > + * from premature OOM killer. > + */ > + mapping_gfp = mapping_gfp_mask(mapping); > + mapping_set_gfp_mask(mapping, mapping_gfp | __GFP_FS | __GFP_IO); > ret = vma->vm_ops->fault(vma, &vmf); > + mapping_set_gfp_mask(mapping, mapping_gfp); > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) > return ret; -- Michal Hocko SUSE Labs -- 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>