Received-SPF: pass (google.com: domain of linux-kernel+bounces-205737-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Message-ID: <6b39db70-70ee-4370-acc3-86050562e343@gmail.com>
Date: Fri, 7 Jun 2024 17:33:44 +0800
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [RFC 1/3] mm/ksm: add anonymous check in find_mergeable_vma
To: David Hildenbrand <david@redhat.com>, alexs@kernel.org,
 Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
 linux-kernel@vger.kernel.org, izik.eidus@ravellosystems.com,
 willy@infradead.org, aarcange@redhat.com, chrisw@sous-sol.org,
 hughd@google.com
References: <20240605095304.66389-1-alexs@kernel.org>
 <353d4f6c-ed3d-4afe-82ab-8c0b22a0178f@redhat.com>
Content-Language: en-US
From: Alex Shi <seakeel@gmail.com>
In-Reply-To: <353d4f6c-ed3d-4afe-82ab-8c0b22a0178f@redhat.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit


On 6/5/24 5:56 PM, David Hildenbrand wrote:
> On 05.06.24 11:53, alexs@kernel.org wrote:
>> From: "Alex Shi (tencent)" <alexs@kernel.org>
>>
>> We do vma_set_anonyous in do_mmap(), and then vma_is_anonymous()
>> checking workable, use it as a extra check since ksm only care anonymous
>> pages.
>>
>> Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
>> ---
>>   mm/ksm.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/ksm.c b/mm/ksm.c
>> index f5138f43f0d2..088bce39cd33 100644
>> --- a/mm/ksm.c
>> +++ b/mm/ksm.c
>> @@ -742,7 +742,8 @@ static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
>>       if (ksm_test_exit(mm))
>>           return NULL;
>>       vma = vma_lookup(mm, addr);
>> -    if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
>> +    if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma ||
>> +            !vma_is_anonymous(vma))
> 
> Doesn't KSM also apply to COW'ed pages in !anon mappings? At least that's what I recall.
I didn't a evidence for this. :( 

In write_protect_page(), "PageAnonExclusive(&folio->page);" has a "VM_BUG_ON_PGFLAGS(!PageAnon(page), page);"
So is this hints the vma also need to be anonymous one?


Thanks a lot!
Alex
>