[Crash-utility] [External Mail]Re: zram decompress support for gcore/crash-utility

[Dave Anderson]

----- Original Message -----
> Hi,Dave
> zram is same with other swap device,but every swaped page will be compressed then saved to another memory address.
> The process is same with the common swap device,non-swap just a normal user address,pgd and mmu will translate to phy address
> 
> please refer to below information:
> crash> vm -p
> PID: 1565   TASK: ffffffe1fce32d00  CPU: 7   COMMAND: "system_server"
>        MM               PGD          RSS    TOTAL_VM
> ffffffe264431c00  ffffffe1f54ad000  528472k  9780384k
>       VMA           START       END     FLAGS FILE
> ffffffe0ea401300   12c00000   12e00000 100073
> VIRTUAL     PHYSICAL
> ...
> 144fc000    SWAP: /dev/block/zram0  OFFSET: 236750
> ...
> 1738e000    SWAP: /dev/block/zram0  OFFSET: 73426
> 1738f000           21aa2c000
> 17390000           1c3308000
> 17391000    SWAP: /dev/block/zram0  OFFSET: 73431
> 17392000           19c162000
> 17393000           19c132000
> 17394000    SWAP: /dev/block/zram0  OFFSET: 234576
> 17395000           19c369000
> 17396000           20b35c000
> 17397000           18011e000
> 17398000    SWAP: /dev/block/zram0  OFFSET: 73433
> 17399000           1dc3d2000
> 1739a000           1bc59f000
> 1739b000    SWAP: /dev/block/zram0  OFFSET: 73437
> 
> 
> crash> vtop -c 1565 144fc000
> VIRTUAL     PHYSICAL
> 144fc000    (not mapped)
> 
> PAGE DIRECTORY: ffffffe1f54ad000
>    PGD: ffffffe1f54ad000 => 1f54ab003
>    PMD: ffffffe1f54ab510 => 1f43b8003
>    PTE: ffffffe1f43b87e0 => 39cce00
> 
>   PTE          SWAP        OFFSET
> 39cce00  /dev/block/zram0  236750
> 
>       VMA           START       END     FLAGS FILE
> ffffffe148bafe40   144c0000   14540000 100073
> 
> SWAP: /dev/block/zram0  OFFSET: 236750

Ok, so with respect to user-space virtual addresses, there is nothing
other than handling zram swap-backed memory.

So what you're proposing is that when reading user-space memory
that happens to be backed-up on a zram swap device, then the user
data could alternatively be read from the zram swap device, and
presented as if it were present in physical memory?

Are the physical RAM pages that make up the contents of a zram
device collected with a typical filtered compressed kdump?  If not,
what makedumpfile -d flag is required for them to be captured?

Dave