Hi,Dave
Zram is a virtual device,it simulated as a block device,it's part of
memroy/ramdump,just enable  CONFIG_ZRAM,no other settings needed.
you can refer to drivers/block/zram/zram_drv.c
driver calling zram_meta_alloc to alloc memory from RAM.
We want to be able to access these zram page like a normal page.
________________________________________
From: Dave Anderson <anderson(a)redhat.com>
Sent: Wednesday, April 1, 2020 23:24
To: 赵乾利
Cc: d hatayama; Discussion list for crash utility usage, maintenance and development
Subject: Re: [External Mail]Re: [Crash-utility] 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
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