On Mon, Feb 07, 2022 at 07:22:22PM -0800, Hugh Dickins wrote: > On Fri, 28 Jan 2022, CGEL wrote: > > 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(). > > I'm entirely PSI-ignorant, and reluctant to disagree with Johannes, > but I don't see how your patch to ksm_might_need_to_copy() could be > correct - maybe the "swapping" in your subject is confusing. > > There is no PSI enter and exit around the page allocation and copying > in wp_page_copy(), so why in the analogous ksm_might_need_to_copy()? > I think it's two questions, first why PSI didn't treat wp_page_copy() as memstall, second why should PSI treat ksm_might_need_to_copy() as memstall. The first question is unrelated with this patch. I think the reason is PSI focous on memory contending(see Documentation/accounting/psi.rst), and wp_page_copy() is not caused by memory contending. Actually wp_page_copy() will still be called if memory is not contending. For the second question, ksm_might_need_to_copy() is called only becaused of swapping, and swap is caused by memory contending, so PSI better treat it as memstall. Thanks. > Hugh
