linux-kernel - Re: [PATCH V2] mm/mprotect: Add a cond_resched() inside change_pmd

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Message-Id: <28e54a80-73d9-76aa-31d5-f71375f14b96@linux.vnet.ibm.com>
Date:   Thu, 14 Dec 2017 18:25:54 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org
Subject: Re: [PATCH V2] mm/mprotect: Add a cond_resched() inside
 change_pmd_range()

On 12/14/2017 04:59 PM, Michal Hocko wrote:
> On Thu 14-12-17 16:44:26, Anshuman Khandual wrote:
>> diff --git a/mm/mprotect.c b/mm/mprotect.c
>> index ec39f73..43c29fa 100644
>> --- a/mm/mprotect.c
>> +++ b/mm/mprotect.c
>> @@ -196,6 +196,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
>>  		this_pages = change_pte_range(vma, pmd, addr, next, newprot,
>>  				 dirty_accountable, prot_numa);
>>  		pages += this_pages;
>> +		cond_resched();
>>  	} while (pmd++, addr = next, addr != end);
>>  
>>  	if (mni_start)
> 
> this is not exactly what I meant. See how change_huge_pmd does continue.
> That's why I mentioned zap_pmd_range which does goto next...

I might be still missing something but is this what you meant ?
Here we will give cond_resched() cover to the THP backed pages
as well.

diff --git a/mm/mprotect.c b/mm/mprotect.c
index ec39f73..3d445ee 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -188,7 +188,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
                                        }
 
                                        /* huge pmd was handled */
-                                       continue;
+                                       goto next;
                                }
                        }
                        /* fall through, the trans huge pmd just split */
@@ -196,6 +196,8 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
                this_pages = change_pte_range(vma, pmd, addr, next, newprot,
                                 dirty_accountable, prot_numa);
                pages += this_pages;
+next:
+               cond_resched();
        } while (pmd++, addr = next, addr != end);
 
        if (mni_start)