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From: Qian Cai <cai@lca.pw>
To: Michal Hocko <mhocko@kernel.org>
Cc: akpm@linux-foundation.org, Pavel.Tatashin@microsoft.com,
	mingo@kernel.org, hpa@zytor.com, mgorman@techsingularity.net,
	iamjoonsoo.kim@lge.com, yang.shi@linaro.org, tglx@linutronix.de,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] mm/page_owner: fix for deferred struct page init
Date: Thu, 3 Jan 2019 12:38:59 -0500	[thread overview]
Message-ID: <5d8f3a98-a954-c8ab-83d9-2f94c614f268@lca.pw> (raw)
In-Reply-To: <20190103165927.GU31793@dhcp22.suse.cz>

On 1/3/19 11:59 AM, Michal Hocko wrote:
>> As mentioned above, "If deselected DEFERRED_STRUCT_PAGE_INIT, it is still better
>> to call page_ext_init() earlier, so page owner could catch more early page
>> allocation call sites."
> 
> Do you have any numbers to show how many allocation are we losing that
> way? In other words, do we care enough to create an ugly code?

Well, I don't have any numbers, but I read that Joonsoo did not really like to
defer page_ext_init() unconditionally.

"because deferring page_ext_init() would make page owner which uses page_ext
miss some early page allocation callsites. Although it already miss some early
page allocation callsites, we don't need to miss more."

https://lore.kernel.org/lkml/20160524053714.GB32186@js1304-P5Q-DELUXE/

>>>> diff --git a/mm/page_ext.c b/mm/page_ext.c
>>>> index ae44f7adbe07..d76fd51e312a 100644
>>>> --- a/mm/page_ext.c
>>>> +++ b/mm/page_ext.c
>>>> @@ -399,9 +399,8 @@ void __init page_ext_init(void)
>>>>  			 * -------------pfn-------------->
>>>>  			 * N0 | N1 | N2 | N0 | N1 | N2|....
>>>>  			 *
>>>> -			 * Take into account DEFERRED_STRUCT_PAGE_INIT.
>>>>  			 */
>>>> -			if (early_pfn_to_nid(pfn) != nid)
>>>> +			if (pfn_to_nid(pfn) != nid)
>>>>  				continue;
>>>>  			if (init_section_page_ext(pfn, nid))
>>>>  				goto oom;
>>>
>>> Also this doesn't seem to be related, right?
>>
>> No, it is related. Because of this patch, page_ext_init() is called after all
>> the memory has already been initialized,
>> so no longer necessary to call early_pfn_to_nid().
> 
> Yes, but it looks like a follow up cleanup/optimization to me.

That early_pfn_to_nid() was introduced in fe53ca54270 (mm: use early_pfn_to_nid
in page_ext_init) which also messed up the order of page_ext_init() in
start_kernel(), so this patch basically revert that commit.

  reply	other threads:[~2019-01-03 17:39 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1545172285.18411.26.camel@lca.pw>
2018-12-19  1:57 ` [PATCH] mm: skip checking poison pattern for page_to_nid() Qian Cai
2018-12-19 10:20   ` Michal Hocko
2018-12-19 12:46     ` Qian Cai
2018-12-20  6:03       ` [PATCH] mm/page_owner: fix for deferred struct page init Qian Cai
2018-12-20  9:22         ` Michal Hocko
2018-12-20 18:50           ` [PATCH v2] " Qian Cai
2018-12-20 20:31             ` [PATCH v3] " Qian Cai
2018-12-20 21:00               ` William Kucharski
2018-12-20 21:04                 ` Qian Cai
2019-01-03 11:51               ` Michal Hocko
2019-01-03 16:38                 ` Qian Cai
2019-01-03 16:59                   ` Michal Hocko
2019-01-03 17:38                     ` Qian Cai [this message]
2019-01-03 19:07                       ` Michal Hocko
2019-01-03 19:53                         ` Qian Cai
2019-01-03 20:22                           ` Michal Hocko
2019-01-03 22:22                             ` Qian Cai
2019-01-04 13:09                               ` Michal Hocko
2019-01-04 15:01                                 ` Qian Cai
2019-01-04 15:17                                   ` Michal Hocko
2019-01-04 15:25                                     ` Qian Cai
2019-01-04 15:32                                       ` Michal Hocko
2019-01-04 20:18                                         ` Qian Cai
2019-01-07 18:43                                           ` Michal Hocko
2019-01-08  1:53                                             ` Qian Cai
2019-01-08  8:20                                               ` Michal Hocko
2019-01-08 13:19                                                 ` Qian Cai
2019-01-08 22:02                                                   ` Andrew Morton
2019-01-08 22:13                                                     ` Qian Cai
2019-01-08 22:40                                                       ` Michal Hocko
2019-01-09  7:34             ` [PATCH v2] " Michal Hocko
2019-01-15 20:28               ` [PATCH] Revert "mm: use early_pfn_to_nid in page_ext_init" Qian Cai

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