[Crash-utility] zram decompress support for gcore/crash-utility

[Dave Anderson]

----- Original Message -----

...

> > 
> > As far as the gcore extension module, that is maintained by Daisuke Hatayama,
> > and he make all decisions w/respect to that codebase.  I've cc'd this response
> > to him.
> 
> Thanks Zhao for your patch set.
> Thanks for ccing me, Dave.
> 
> I agree that ZRAM support is useful as your explanation. On the other
> hand, it is not only for crash gcore command, but also for crash utility. I think
> it more natural than the current implementation of your patch set that you
> implement a ZRAM support in crash utility and then do it in crash gcore command.
> 
> If the ZRAM support were transparent to readmem() interface, there would be no need
> to implement crash gcore command at all. If not, there would be need to add a new code
> for the ZRAM support just corresponding to the following stanza in
> 0001-gcore-add-support-zram-swap.patch:
> 
> @@ -225,6 +417,18 @@ void gcore_coredump(void)
>                                               strerror(errno));
>                         } else {
>                                 pagefaultf("page fault at %lx\n", addr);
> +                               if (paddr != 0) {
> +                                       pte_val = paddr;
> +                                       if(try_zram_decompress(pte_val, (unsigned char *)buffer) == PAGE_SIZE)
> +                                       {
> +                                               error(WARNING, "zram decompress successed\n");
> +                                               if (fwrite(buffer, PAGE_SIZE, 1, gcore->fp) != 1)
> +                                                       error(FATAL, "%s: write: %s\n", gcore->corename, strerror(errno));
> +                                               continue;
> +                                       }
> +          
> +                      }

I'm not clear on how zram is linked into the user-space mapping.  For user space that
has been swapped out to a zram swap device, I presume it's the same as is, but it 
references the zram swap device.  But for other user-space mappings (non-swapped),
what does the "vm -p" display for user space virtual address pages that are backed
by zram?  And for that matter, what does "vtop <address>" show?

Thanks,
  Dave