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

[Dave Anderson]

----- Original Message -----
> 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.

I understand all that.  I'm just curious how makedumpfile will handle/filter
the physical RAM pages that make up the zram block device.

Anyway, send a patch and I'll take a look.

Dave


> 
> ________________________________________
> From: Dave Anderson <anderson at 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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