From: Qian Cai <cai@lca.pw>
To: Michal Hocko <mhocko@kernel.org>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC
Date: Tue, 26 Feb 2019 09:16:30 -0500 [thread overview]
Message-ID: <4d4d3140-6d83-6d22-efdb-370351023aea@lca.pw> (raw)
In-Reply-To: <20190226123521.GZ10588@dhcp22.suse.cz>
On 2/26/19 7:35 AM, Michal Hocko wrote:
> On Mon 25-02-19 14:17:10, Qian Cai wrote:
>> When onlining memory pages, it calls kernel_unmap_linear_page(),
>> However, it does not call kernel_map_linear_page() while offlining
>> memory pages. As the result, it triggers a panic below while onlining on
>> ppc64le as it checks if the pages are mapped before unmapping,
>> Therefore, let it call kernel_map_linear_page() when setting all pages
>> as reserved.
>
> This really begs for much more explanation. All the pages should be
> unmapped as they get freed AFAIR. So why do we need a special handing
> here when this path only offlines free pages?
>
It sounds like this is exact the point to explain the imbalance. When offlining,
every page has already been unmapped and marked reserved. When onlining, it
tries to free those reserved pages via __online_page_free(). Since those pages
are order 0, it goes free_unref_page() which in-turn call
kernel_unmap_linear_page() again without been mapped first.
next prev parent reply other threads:[~2019-02-26 14:16 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-25 19:17 Qian Cai
2019-02-26 12:13 ` Souptick Joarder
2019-02-26 14:07 ` Qian Cai
2019-02-26 12:35 ` Michal Hocko
2019-02-26 14:16 ` Qian Cai [this message]
2019-02-26 14:23 ` Michal Hocko
2019-02-26 17:53 ` Qian Cai
2019-02-26 18:16 ` Michal Hocko
2019-02-26 18:20 ` Michal Hocko
2019-02-26 19:19 ` Qian Cai
2019-02-26 19:40 ` Michal Hocko
2019-02-26 20:10 ` Qian Cai
2019-02-26 20:40 ` Michal Hocko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4d4d3140-6d83-6d22-efdb-370351023aea@lca.pw \
--to=cai@lca.pw \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox