Re: System freezes after OOM

[Michal Hocko <mhocko@kernel.org>]

On Wed 13-07-16 13:10:06, Michal Hocko wrote:
> On Tue 12-07-16 19:44:11, Mikulas Patocka wrote:
[...]
> > As long as swapping is in progress, the free memory is below the limit 
> > (because the swapping activity itself consumes any memory over the limit). 
> > And that triggered the OOM killer prematurely.
> 
> I am not sure I understand the last part. Are you saing that we trigger
> OOM because the initiated swapout will not be able to finish the IO thus
> release the page in time?
> 
> The oom detection checks waits for an ongoing writeout if there is no
> reclaim progress and at least half of the reclaimable memory is either
> dirty or under writeback. Pages under swaout are marked as under
> writeback AFAIR. The writeout path (dm-crypt worker in this case) should
> be able to allocate a memory from the mempool, hand over to the crypt
> layer and finish the IO. Is it possible this might take a lot of time?

I am not familiar with the crypto API but from what I understood from
crypt_convert the encryption is done asynchronously. Then I got lost in
the indirection. Who is completing the request and from what kind of
context? Is it possible it wouldn't be runable for a long time?
-- 
Michal Hocko
SUSE Labs