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

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&gt; 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 #/******本邮件及其附件含有小米公司的保密信息，仅限于发送给上面地址中列出的个人或群组。禁止任何其他人以任何形式使用（包括但不限于全部或部分地泄露、复制、或散发）本邮件中的信息。如果您错收了本邮件，请您立即电话或邮件通知发件人并删除本邮件！ This e-mail and its attachments contain confidential information from XIAOMI, which is intended only for the person or entity whose address is listed above. Any use of the information contained herein in any way (including, but not limited to, total or partial disclosure, reproduction, or dissemination) by persons other than the intended recipient(s) is prohibited. If you receive this e-mail in error, please notify the sender by phone or email immediately and delete it!******/#