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From: Michal Hocko <mhocko@kernel.org>
To: Oscar Salvador <osalvador@suse.de>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	mike.kravetz@oracle.com, zi.yan@cs.rutgers.edu,
	akpm@linux-foundation.org
Subject: Re: [PATCH] mm/isolation: Remove redundant pfn_valid_within() in __first_valid_page()
Date: Thu, 21 Mar 2019 11:03:16 +0100	[thread overview]
Message-ID: <20190321100316.GN8696@dhcp22.suse.cz> (raw)
In-Reply-To: <20190321094237.onu3kar2ez7xv5wj@d104.suse.de>

On Thu 21-03-19 10:42:40, Oscar Salvador wrote:
> On Thu, Mar 21, 2019 at 09:43:15AM +0530, Anshuman Khandual wrote:
> > pfn_valid_within() calls pfn_valid() when CONFIG_HOLES_IN_ZONE making it
> > redundant for both definitions (w/wo CONFIG_MEMORY_HOTPLUG) of the helper
> > pfn_to_online_page() which either calls pfn_valid() or pfn_valid_within().
> > pfn_valid_within() being 1 when !CONFIG_HOLES_IN_ZONE is irrelevant either
> > way. This does not change functionality.
> > 
> > Fixes: 2ce13640b3f4 ("mm: __first_valid_page skip over offline pages")
> > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> 
> About the "Fixes:" tag issue, I agree with Michal that the code is not
> really broken, but perhaps "suboptimal" depending on how much can affect
> performance on those systems where pfn_valid_within() is more complicated than
> simple returning true.
> 
> I see that on arm64, that calls memblock_is_map_memory()->memblock_search(),
> to trigger a search for the region containing the address, so I guess it
> is an expensive operation.
> 
> Depending on how much time we can shave, it might be worth to have the tag
> Fixes, but the removal of the code is fine anyway, so:

Yeah, seeing a noticesable slowdown (actual numbers) would warrant a
backport to 5.0.

-- 
Michal Hocko
SUSE Labs

  reply	other threads:[~2019-03-21 10:03 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-21  4:13 [PATCH] mm/isolation: Remove redundant pfn_valid_within() in __first_valid_page() Anshuman Khandual
2019-03-21  5:01 ` Zi Yan
2019-03-21  5:33   ` Anshuman Khandual
2019-03-21  8:07     ` Michal Hocko
2019-03-21  8:13       ` Anshuman Khandual
2019-03-21  9:42 ` Oscar Salvador
2019-03-21 10:03   ` Michal Hocko [this message]
2019-03-22  9:23 ` Michal Hocko

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