linux-kernel - RE: [PATCH 1/2 v4] kdump: add the vmcoreinfo documentation

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Date:   Fri, 4 Jan 2019 15:31:28 +0000
From:   Kazuhito Hagio <k-hagio@...jp.nec.com>
To:     lijiang <lijiang@...hat.com>
CC:     "bhe@...hat.com" <bhe@...hat.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "dyoung@...hat.com" <dyoung@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2 v4] kdump: add the vmcoreinfo documentation

-----Original Message-----
> >> +=======================
> >> +What is the VMCOREINFO?
> >> +=======================
> >> +
> >> +VMCOREINFO is a special ELF note section. It contains various
> >> +information from the kernel like structure size, page size, symbol
> >> +values, field offsets, etc. These data are packed into an ELF note
> >> +section and used by user-space tools like crash and makedumpfile to
> >> +analyze a kernel's memory layout.
> >> +
> >> +To dump the VMCOREINFO contents, one can do:
> >> +
> >> +# makedumpfile -g VMCOREINFO -x vmlinux
> >
> > again, this command does not dump the VMCOREINFO in ELF note section.
> > It converts the vmlinux's debug infomation into a VMCOREINFO-like data.
> > So I don't think this command is suitable to introduce here.
> >
> 
> Thank you, Kazu.
> 
> As you mentioned, makedumpfile in 'devel' branch can print VMCOREINFO in /proc/kcore,
> can i add the following command to this document?
> 
> #makedumpfile --mem-usage /proc/kcore -D

I don't know whether we can add unreleased softwares to the document.
Any comments on this?

If it's OK, crash also can dump it, so
---
To dump the VMCOREINFO contents, one can do:

  # crash vmlinux /proc/kcore
  ...
  > help -n
or
  # makedumpfile -D --mem-usage /proc/kcore
---

or remove that for now and update later?

> 
> >> +PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_slab|
> >> +PG_hwpoision|PG_head_mask
> >> +-----------------------------------------------------
> >> +
> >> +Page attributes. These flags are used to filter free pages.
> >
> > Some of these are not used to filter *free* pages, so
> >
> > ... used to filter various unnecessary pages.
> >
> 
> Great. I will modify it in next post.
> 
> And also merge the 'PG_buddy' and 'PG_offline'  into the PG_* flag here.

Thanks, I think your "PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline)" style is good.

Kazu

> 
> Many thanks.
> 
> Lianbo
> 
> >> +PAGE_BUDDY_MAPCOUNT_VALUE or ~PG_buddy
> >> +--------------------------------------
> >
> > then, this can be merged into the one above?
> >
> >> +======
> >> +x86_64
> >> +======
> > ...
> >> +PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline)
> >> +----------------------------------------
> >
> > This looks not only for x86_64, and also can be merged into
> > the PG_* flags?
> >
> > Thank you for your effort!
> > Kazu
> >
> >