Hi, Hugh, Hugh Dickins <hughd@xxxxxxxxxx> writes: > On Thu, 31 Jan 2019, Andrew Morton wrote: >> On Thu, 31 Jan 2019 10:48:29 +0800 "Huang\, Ying" <ying.huang@xxxxxxxxx> wrote: >> > Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: >> > > mm-swap-fix-race-between-swapoff-and-some-swap-operations.patch is very >> > > stuck so can you please redo this against mainline? >> > >> > Allow me to be off topic, this patch has been in mm tree for quite some >> > time, what can I do to help this be merged upstream? > > Wow, yes, it's about a year old. > >> >> I have no evidence that it has been reviewed, for a start. I've asked >> Hugh to look at it. > > I tried at the weekend. Usual story: I don't like it at all, the > ever-increasing complexity there, but certainly understand the need > for that fix, and have not managed to think up anything better - > and now I need to switch away, sorry. > > The multiple dynamically allocated and freed swapper address spaces > have indeed broken what used to make it safe. If those imaginary > address spaces did not have to be virtually contiguous, I'd say > cache them and reuse them, instead of freeing. But I don't see > how to do that as it stands. > > find_get_page(swapper_address_space(entry), swp_offset(entry)) has > become an unsafe construct, where it used to be safe against corrupted > page tables. Maybe we don't care so much about crashing on corrupted > page tables nowadays (I haven't heard recent complaints), and I think > Huang is correct that lookup_swap_cache() and __read_swap_cache_async() > happen to be the only instances that need to be guarded against swapoff > (the others are working with page table locked). > > The array of arrays of swapper spaces is all just to get a separate > lock for separate extents of the swapfile: I wonder whether Matthew has > anything in mind for that in XArray (I think Peter once got it working > in radix-tree, but the overhead not so good). > > (I was originally horrified by the stop_machine() added in swapon and > swapoff, but perhaps I'm remembering a distant past of really stopping > the machine: stop_machine() today looked reasonable, something to avoid > generally like lru_add_drain_all(), but not as shameful as I thought.) Thanks a lot for your review and comments! It appears that you have no strong objection for this patch? Could I have your "Acked-by"? Best Regards, Huang, Ying
