Messages in this thread | | | Date | Tue, 28 Feb 2023 08:37:25 +0100 | From | Andrew Jones <> | Subject | Re: [PATCH v4 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk |
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On Tue, Feb 28, 2023 at 07:29:40AM +0000, JeeHeng Sia wrote: > > > > -----Original Message----- > > From: Andrew Jones <ajones@ventanamicro.com> > > Sent: Tuesday, 28 February, 2023 3:19 PM > > To: JeeHeng Sia <jeeheng.sia@starfivetech.com> > > Cc: paul.walmsley@sifive.com; palmer@dabbelt.com; aou@eecs.berkeley.edu; linux-riscv@lists.infradead.org; linux- > > kernel@vger.kernel.org; Leyfoon Tan <leyfoon.tan@starfivetech.com>; Mason Huo <mason.huo@starfivetech.com> > > Subject: Re: [PATCH v4 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk > > > > On Tue, Feb 28, 2023 at 05:33:32AM +0000, JeeHeng Sia wrote: > > > > > > > > > > -----Original Message----- > > > > From: Andrew Jones <ajones@ventanamicro.com> > > > > Sent: Tuesday, 28 February, 2023 1:05 PM > > > > To: JeeHeng Sia <jeeheng.sia@starfivetech.com> > > > > Cc: paul.walmsley@sifive.com; palmer@dabbelt.com; aou@eecs.berkeley.edu; linux-riscv@lists.infradead.org; linux- > > > > kernel@vger.kernel.org; Leyfoon Tan <leyfoon.tan@starfivetech.com>; Mason Huo <mason.huo@starfivetech.com> > > > > Subject: Re: [PATCH v4 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk > > > > > > > > On Tue, Feb 28, 2023 at 01:32:53AM +0000, JeeHeng Sia wrote: > > > > > > > > > load image; > > > > > > > > > loop: Create pbe chain, return error if failed; > > > > > > > > > > > > > > > > This loop pseudocode is incomplete. It's > > > > > > > > > > > > > > > > loop: > > > > > > > > if (swsusp_page_is_forbidden(page) && swsusp_page_is_free(page)) > > > > > > > > return page_address(page); > > > > > > > > Create pbe chain, return error if failed; > > > > > > > > ... > > > > > > > > > > > > > > > > which I pointed out explicitly in my last reply. Also, as I asked in my > > > > > > > > last reply (and have been asking four times now, albeit less explicitly > > > > > > > > the first two times), how do we know at least one PBE will be linked? > > > > > > > 1 PBE correspond to 1 page, you shouldn't expect only 1 page is saved. > > > > > > > > > > > > I know PBEs correspond to pages. *Why* should I not expect only one page > > > > > > is saved? Or, more importantly, why should I expect more than zero pages > > > > > > are saved? > > > > > > > > > > > > Convincing answers might be because we *always* put the restore code in > > > > > > pages which get added to the PBE list or that the original page tables > > > > > > *always* get put in pages which get added to the PBE list. It's not very > > > > > > convincing to simply *assume* that at least one random page will always > > > > > > meet the PBE list criteria. > > > > > > > > > > > > > Hibernation core will do the calculation. If the PBEs (restore_pblist) linked successfully, the hibernated image will be restore > > else > > > > > > normal boot will take place. > > > > > > > > Or, even more specifically this time, where is the proof that for each > > > > > > > > hibernation resume, there exists some page such that > > > > > > > > !swsusp_page_is_forbidden(page) or !swsusp_page_is_free(page) is true? > > > > > > > forbidden_pages and free_pages are not contributed to the restore_pblist (as you already aware from the code). Infact, the > > > > > > forbidden_pages and free_pages are not save into the disk. > > > > > > > > > > > > Exactly, so those pages are *not* going to contribute to the greater than > > > > > > zero pages. What I've been asking for, from the beginning, is to know > > > > > > which page(s) are known to *always* contribute to the list. Or, IOW, how > > > > > > do you know the PBE list isn't empty, a.k.a restore_pblist isn't NULL? > > > > > Well, this is keep going around in a circle, thought the answer is in the hibernation code. restore_pblist get the pointer from the > > PBE, > > > > and the PBE already checked for validity. > > > > > > > > It keeps going around in circles because you keep avoiding my question by > > > > pointing out trivial linked list code. I'm not worried about the linked > > > > list code being correct. My concern is that you're using a linked list > > > > with an assumption that it is not empty. My question has been all along, > > > > how do you know it's not empty? > > > > > > > > I'll change the way I ask this time. Please take a look at your PBE list > > > > and let me know if there are PBEs on it that must be there on each > > > > hibernation resume, e.g. the resume code page is there or whatever. > > > > > > > > > Can I suggest you to submit a patch to the hibernation core? > > > > > > > > Why? What's wrong with it? > > > Kindly let me draw 2 scenarios for you. Option 1 is to add the restore_pblist checking to the hibernation core and option 2 is to add > > restore_pblist checking to the arch solution > > > Although I really don't think it is needed. But if you really wanted to add the checking, I would suggest to go with option 1. again, I > > really think that it is not needed! > > > > This entire email thread is because you've first coded, and now stated, > > that you don't think the PBE list will ever be empty. And now, below, I > > see you're proposing to return an error when the PBE list is empty, why? > > If there's nothing in the PBE list, then there's nothing to do for it. > > Why is that an error condition? > > > > Please explain to me why you think the PBE list *must* not be empty > > (which is what I've been asking for over and over). OIOW, are there > > any pages you have in mind which the resume kernel always uses and > > are also always going to end up in the suspend image? I don't know, > > but I assume clean, file-backed pages do not get added to the suspend > > image, which would rule out most kernel code pages. Also, many pages > > written during boot (which is where the resume kernel is at resume time) > > were no longer resident at hibernate time, so they won't be in the > > suspend image either. While it's quite likely I'm missing something > > obvious, I'd rather be told what that is than to assume the PBE list > > will never be empty. Which is why I keep asking about it... > The answer already in the Linux kernel hibernation core, do you need me to write a white paper to explain in detail or you need a conference call?
I'm not sure why you don't just write a paragraph or two here in this email thread explaining what "the answer" is. Anyway, feel free to invite me to a call if you think it'd be easier to hash out that way.
Thanks, drew
> > > > Thanks, > > drew > > > > > > > > //Option 1 > > > //Pseudocode to illustrate the image loading > > > initialize restore_pblist to null; > > > initialize safe_pages_list to null; > > > Allocate safe page list, return error if failed; > > > load image; > > > loop: Create pbe chain, return error if failed; > > > assign orig_addr and safe_page to pbe; > > > link pbe to restore_pblist; > > > /* Add checking here */ > > > return error if restore_pblist equal to null; > > > return pbe to handle->buffer; > > > check handle->buffer; > > > goto loop if no error else return with error; > > > > > > //option 2 > > > //Pseudocode to illustrate the image loading > > > initialize restore_pblist to null; > > > initialize safe_pages_list to null; > > > Allocate safe page list, return error if failed; > > > load image; > > > loop: Create pbe chain, return error if failed; > > > assign orig_addr and safe_page to pbe; > > > link pbe to restore_pblist; > > > return pbe to handle->buffer; > > > check handle->buffer; > > > goto loop if no error else return with error; > > > everything works correctly, continue the rest of the operation > > > invoke swsusp_arch_resume > > > > > > //@swsusp_arch_resume() > > > loop2: return error if restore_pblist is null > > > increment restore_pblist and goto loop2 > > > create temp_pg_table > > > continue the rest of the resume operation > > > > > > > > Thanks, > > > > drew
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