Re: [RFC PATCH 2/3] hugetlb: do not update address in huge_pmd_unshare

From: Mike Kravetz <mike.kravetz@oracle.com>
To: Muchun Song <songmuchun@bytedance.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Michal Hocko <mhocko@suse.com>, Peter Xu <peterx@redhat.com>,
	Naoya Horiguchi <naoya.horiguchi@linux.dev>,
	James Houghton <jthoughton@google.com>,
	Mina Almasry <almasrymina@google.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH 2/3] hugetlb: do not update address in huge_pmd_unshare
Date: Tue, 31 May 2022 10:06:51 -0700	[thread overview]
Message-ID: <069d55ca-ca62-0841-b52f-c4352f37959a@oracle.com> (raw)
In-Reply-To: <YpTki4Tvv2muTeJu@FVFYT0MHHV2J.googleapis.com>

On 5/30/22 08:36, Muchun Song wrote:
> On Fri, May 27, 2022 at 03:58:48PM -0700, Mike Kravetz wrote:
>> As an optimization for loops sequentially processing hugetlb address
>> ranges, huge_pmd_unshare would update a passed address if it unshared a
>> pmd.  Updating a loop control variable outside the loop like this is
>> generally a bad idea.  These loops are now using hugetlb_mask_last_hp
> 
> Totally agree.
> 
>> to optimize scanning when non-present ptes are discovered.  The same
>> can be done when huge_pmd_unshare returns 1 indicating a pmd was
>> unshared.
>>
>> Remove address update from huge_pmd_unshare.  Change the passed argument
>> type and update all callers.  In loops sequentially processing addresses
>> use hugetlb_mask_last_hp to update address if pmd is unshared.
>>
>> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> 
> Acked-by: Muchun Song <songmuchun@bytedance.com>
> 
> Some nits below.
> 
>>  		ptep = huge_pte_offset(mm, address, sz);
>>  		if (!ptep)
>>  			continue;
>>  		ptl = huge_pte_lock(h, mm, ptep);
>>  		/* We don't want 'address' to be changed */
> 
> Dead comment, should be removed.

Thanks!  I missed that.

-- 
Mike Kravetz