Messages in this thread | | | Date | Thu, 27 Jan 2022 20:29:08 -0500 | From | Johannes Weiner <> | Subject | Re: [PATCH] psi: Treat ksm swapping in copy as memstall |
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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.
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
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