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

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Date:   Thu, 3 Jan 2019 19:28:14 +0000
From:   Kazuhito Hagio <k-hagio@...jp.nec.com>
To:     Lianbo Jiang <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

Hi Lianbo,

-----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.

> +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.

> +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