HTTPS clone URL
Subversion checkout URL
Please sign in to comment.
swap: fix shmem swapping when more than 8 areas
commit 9b15b81 upstream. Minchan Kim reports that when a system has many swap areas, and tmpfs swaps out to the ninth or more, shmem_getpage_gfp()'s attempts to read back the page cannot locate it, and the read fails with -ENOMEM. Whoops. Yes, I blindly followed read_swap_header()'s pte_to_swp_entry( swp_entry_to_pte()) technique for determining maximum usable swap offset, without stopping to realize that that actually depends upon the pte swap encoding shifting swap offset to the higher bits and truncating it there. Whereas our radix_tree swap encoding leaves offset in the lower bits: it's swap "type" (that is, index of swap area) that was truncated. Fix it by reducing the SWP_TYPE_SHIFT() in swapops.h, and removing the broken radix_to_swp_entry(swp_to_radix_entry()) from read_swap_header(). This does not reduce the usable size of a swap area any further, it leaves it as claimed when making the original commit: no change from 3.0 on x86_64, nor on i386 without PAE; but 3.0's 512GB is reduced to 128GB per swapfile on i386 with PAE. It's not a change I would have risked five years ago, but with x86_64 supported for ten years, I believe it's appropriate now. Hmm, and what if some architecture implements its swap pte with offset encoded below type? That would equally break the maximum usable swap offset check. Happily, they all follow the same tradition of encoding offset above type, but I'll prepare a check on that for next. Reported-and-Reviewed-and-Tested-by: Minchan Kim <email@example.com> Signed-off-by: Hugh Dickins <firstname.lastname@example.org> Signed-off-by: Linus Torvalds <email@example.com> Signed-off-by: Ben Hutchings <firstname.lastname@example.org>
- Loading branch information...
1 parent 7e86185 commit e0254df58aa9a0eede8b7f8dc1cb453e8f1e6b5c Hugh Dickins committed with Ben Hutchings
Showing with 9 additions and 11 deletions.