Re: [PATCH v4 4/5] mm/shmem: fix infinite loop when swap in shmem error at swapoff time

[HORIGUCHI NAOYA(堀口 直也)]

On Mon, May 23, 2022 at 07:23:53PM +0800, Miaohe Lin wrote:
...
> > 
> > I reproduced the deadloop issues when swapin error occurs at swapoff time in my linux-next-next-20220520 env,
> > and I found this patch could solve the issue now with the fix in my another email.
> > 
> > BTW: When I use dm-dust to inject the swapin IO error, I don't see non-uptodate folio when shmem_swapin_folio
> > and swapoff succeeds. There might be some issues around that module (so I resort to the another way to inject
> > the swapin error), but the patch itself works anyway. ;)
> 
> Sorry, the reason I don't see non-uptodate folio when shmem_swapin_folio is that all the shmem pages are still
> in the swapcache. They're not read from disk so there is no really IO error. :) When they're indeed freed, the
> deadloop issue occurs.
> 
> I am thinking about extending the function of MADV_PAGEOUT to free the swapcache page. The page resides in the
> swapcache does not save the system memory anyway. And this could help test the swapin behavior. But I'm not
> sure whether it's needed.

The extension make MADV_PAGEOUT free swapcaches makes sense to me,
so I'll support it if the original implementer agrees the change.

Thanks,
Naoya Horiguchi