On 25.04.22 09:55, ying.huang@xxxxxxxxx wrote: > 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. Exactly, and IMHO if we have 22 or 23 doesn't make a real difference here ... -- Thanks, David / dhildenb
