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