On Thu, Jan 27, 2022 at 08:29:08PM -0500, Johannes Weiner wrote:
> On Fri, Jan 21, 2022 at 09:51:08AM +0000, CGEL wrote:
> > Wed, Jan 19, 2022 at 07:58:23AM -0500, Johannes Weiner wrote:
> > > On Wed, Jan 19, 2022 at 06:13:54AM +0000, CGEL wrote:
> > > > I did a test, when we use zram, it takes longer time for ksm copying than
> > > > swap_readpage(). Ksm copying average takes 147263ns, swap_readpage()
> > > > average takes 55639ns. So I think this patch is reasonable.
> > >
> > > Ok, that sounds reasonable to me as well. Please add the
> > > PageWorkingset() check and resubmit the patch. Thanks!
> > I am a litte confused about adding PageWorkingset(), since I
> > think ksm_might_need_to_copy() memstall is like swap_readpage()
> > memstall and swap_readpage() doesn't add PageWorkingset().
>
> That's actually a bug! It should do that.
I recently found that too. Please CC to me your new patch, thanks!
And I will send V2 of this patch "psi: Treat ksm swapping in copy
as memstall" with PageWorkingset().
> That psi_memstall_enter() in swap_readpage() was added by commit
> 937790699be9c8100e5358625e7dfa8b32bd33f2. It's for catching the
> scenarios that don't go through submit_bio(). When you look at
> submit_bio(), it counts stalls only if we have workingset pages:
>
> /*
> * If we're reading data that is part of the userspace workingset, count
> * submission time as memory stall. When the device is congested, or
> * the submitting cgroup IO-throttled, submission can be a significant
> * part of overall IO time.
> */
> if (unlikely(bio_op(bio) == REQ_OP_READ &&
> bio_flagged(bio, BIO_WORKINGSET))) {
> unsigned long pflags;
>
> psi_memstall_enter(&pflags);
> submit_bio_noacct(bio);
> psi_memstall_leave(&pflags);
> return;
> }
>
> I hope that clarifies it. I'll send a patch to fix up swap_readpage().
>
> Thanks
