On Mon, 2022-04-25 at 09:49 +0200, David Hildenbrand wrote: > On 25.04.22 09:41, ying.huang@xxxxxxxxx wrote: > > Hi, Miaohe, > > > > On Sun, 2022-04-24 at 17:11 +0800, Miaohe Lin wrote: > > > There is a bug in unuse_pte(): when swap page happens to be unreadable, > > > page filled with random data is mapped into user address space. In case > > > of error, a special swap entry indicating swap read fails is set to the > > > page table. So the swapcache page can be freed and the user won't end up > > > with a permanently mounted swap because a sector is bad. And if the page > > > is accessed later, the user process will be killed so that corrupted data > > > is never consumed. On the other hand, if the page is never accessed, the > > > user won't even notice it. > > > > > > Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> > > > Acked-by: David Hildenbrand <david@xxxxxxxxxx> > > > --- > > > include/linux/swap.h | 7 ++++++- > > > include/linux/swapops.h | 10 ++++++++++ > > > mm/memory.c | 5 ++++- > > > mm/swapfile.c | 11 +++++++++++ > > > 4 files changed, 31 insertions(+), 2 deletions(-) > > > > > > diff --git a/include/linux/swap.h b/include/linux/swap.h > > > index 5553189d0215..b82c196d8867 100644 > > > --- a/include/linux/swap.h > > > +++ b/include/linux/swap.h > > > @@ -55,6 +55,10 @@ static inline int current_is_kswapd(void) > > > * actions on faults. > > > */ > > > > > > +#define SWP_SWAPIN_ERROR_NUM 1 > > > +#define SWP_SWAPIN_ERROR (MAX_SWAPFILES + SWP_HWPOISON_NUM + \ > > > + SWP_MIGRATION_NUM + SWP_DEVICE_NUM + \ > > > + SWP_PTE_MARKER_NUM) > > > > > > > > > > It appears wasteful to use another swap device number. > > Do we really care? > > We currently use 5 bits for swap types, so we have a total of 32. > > SWP_HWPOISON_NUM -> 1 > SWP_MIGRATION_NUM -> 3 > SWP_PTE_MARKER_NUM -> 1 > SWP_DEVICE_NUM -> 4 > SWP_SWAPIN_ERROR_NUM -> 1 > > Which would leave us with 32 - 10 = 22 swap devices. IMHO that's plenty > for real life scenarios. Creating multiple swap partitions on one disk can improve the scalability of swap subsystem, although we usually don't have so many disks for swap. > I'd prefer reworking this when we really run into trouble (and we could > think about using more bits for applicable architectures then, for > select 64bit architectures it might be fairly easily possible). Best Regards, Huang, Ying
