linux-kernel - Re: [PATCH 1/6] mm: ksm: use more folio api in ksm_might_need_to

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Message-ID: <67eedbab-bf15-4bc3-88ce-36fc074393bd@huawei.com>
Date:   Thu, 9 Nov 2023 15:09:53 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH 1/6] mm: ksm: use more folio api in
 ksm_might_need_to_copy()



On 2023/11/8 21:59, Matthew Wilcox wrote:
> On Wed, Nov 08, 2023 at 09:40:09AM +0800, Kefeng Wang wrote:
>>
>>
>> On 2023/11/7 22:24, Matthew Wilcox wrote:
>>> On Tue, Nov 07, 2023 at 09:52:11PM +0800, Kefeng Wang wrote:
>>>>    struct page *ksm_might_need_to_copy(struct page *page,
>>>> -			struct vm_area_struct *vma, unsigned long address)
>>>> +			struct vm_area_struct *vma, unsigned long addr)
>>>>    {
>>>>    	struct folio *folio = page_folio(page);
>>>>    	struct anon_vma *anon_vma = folio_anon_vma(folio);
>>>> -	struct page *new_page;
>>>> +	struct folio *new_folio;
>>>> -	if (PageKsm(page)) {
>>>> -		if (page_stable_node(page) &&
>>>> +	if (folio_test_ksm(folio)) {
>>>> +		if (folio_stable_node(folio) &&
>>>>    		    !(ksm_run & KSM_RUN_UNMERGE))
>>>>    			return page;	/* no need to copy it */
>>>>    	} else if (!anon_vma) {
>>>>    		return page;		/* no need to copy it */
>>>> -	} else if (page->index == linear_page_index(vma, address) &&
>>>> +	} else if (page->index == linear_page_index(vma, addr) &&
>>>
>>> Hmm.  page->index is going away.  What should we do here instead?
>>
>> Do you mean to replace page->index to folio->index, or kill index from
>> struct page?
> 
> I'm asking you what we should do.
> 
> Tail pages already don't have a valid ->index (or ->mapping).
> So presumably we can't see a tail page here today.  But will we in future?

I think we could replace page->index to page_to_pgoff(page).

> 
> Just to remind you, the goal here is:
> 
> struct page {
> 	unsigned long memdesc;
> };
> 

Get your point, that will be great.

> so folios will be the only thing that have a ->index.  I haven't looked
> at this code; I know nothing about it.  But you're changing it, so you
> must have some understanding of it.
>