Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   lizhe.67@bytedance.com
To:     vbabka@suse.cz
Cc:     Jason@zx2c4.com, akpm@linux-foundation.org, corbet@lwn.net,
        keescook@chromium.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        lizefan.x@bytedance.com, lizhe.67@bytedance.com,
        mark-pk.tsai@mediatek.com, mhiramat@kernel.org, mhocko@suse.com,
        rostedt@goodmis.org
Subject: Re: [PATCH v4] page_ext: introduce boot parameter 'early_page_ext'
Date:   Mon, 29 Aug 2022 16:18:37 +0800
Message-Id: <20220829081837.38225-1-lizhe.67@bytedance.com>
In-Reply-To: <68133fc4-7034-c07b-f14b-5b4e73e04d2c@suse.cz>
References: <68133fc4-7034-c07b-f14b-5b4e73e04d2c@suse.cz>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 26 Aug 2022 12:49:25 +0200, vbabka@suse.cz wrote:
>On 8/26/22 06:23, Andrew Morton wrote:
>> On Thu, 25 Aug 2022 18:27:14 +0800 lizhe.67@bytedance.com wrote:
>> 
>>> From: Li Zhe <lizhe.67@bytedance.com>
>>> 
>>> In 'commit 2f1ee0913ce5 ("Revert "mm: use early_pfn_to_nid in page_ext_init"")',
>>> we call page_ext_init() after page_alloc_init_late() to avoid some panic
>>> problem. It seems that we cannot track early page allocations in current
>>> kernel even if page structure has been initialized early.
>>> 
>>> This patch introduce a new boot parameter 'early_page_ext' to resolve this
>>> problem. If we pass it to kernel, function page_ext_init() will be moved
>>> up and feature 'deferred initialization of struct pages' will be disabled
>>> to initialize the page allocator early and prevent from the panic problem
>>> above. It can help us to catch early page allocations. This is useful
>>> especially when we find that the free memory value is not the same right
>>> after different kernel booting.
>>> 
>> 
>> WARNING: modpost: vmlinux.o: section mismatch in reference: early_page_ext_enabled (section: .text.unlikely) -> early_page_ext (section: .meminit.data)
>> WARNING: modpost: vmlinux.o: section mismatch in reference: early_page_ext_enabled (section: .text.unlikely) -> early_page_ext (section: .meminit.data)
>
>Hm it's a very small static inline, shouldn't exist separately anywhere.
>Maybe it's due to that new debug info level thing?
>
>Would this work instead?
>
>----8<----
>diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
>index 884282a7f03a..4bf4e58cf2d4 100644
>--- a/include/linux/page_ext.h
>+++ b/include/linux/page_ext.h
>@@ -40,7 +40,7 @@ extern bool early_page_ext;
> extern unsigned long page_ext_size;
> extern void pgdat_page_ext_init(struct pglist_data *pgdat);
> 
>-static inline bool early_page_ext_enabled(void)
>+static inline bool __meminit early_page_ext_enabled(void)
> {
> 	return early_page_ext;
> }

I think this is also a method to solve this problem.
Due to '__meminit', early_page_ext_enabled() can not be an inline function
now. So if we finally choose this method, I suggest we put function
early_page_ext_enabled() into page_ext.c if CONFIG_PAGE_EXTENSION=y, and
we can make 'early_page_ext' a static variable.