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Date:   Thu, 14 Jan 2021 11:26:31 +0800
From:   zhong jiang <zhongjiang-ali@...ux.alibaba.com>
To:     Ruan Shiyang <ruansy.fnst@...fujitsu.com>, Jan Kara <jack@...e.cz>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-raid@...r.kernel.org,
        darrick.wong@...cle.com, dan.j.williams@...el.com,
        david@...morbit.com, hch@....de, song@...nel.org, rgoldwyn@...e.de,
        qi.fuli@...itsu.com, y-goto@...itsu.com
Subject: Re: [PATCH 04/10] mm, fsdax: Refactor memory-failure handler for dax
 mapping


On 2021/1/14 9:44 上午, Ruan Shiyang wrote:
>
>
> On 2021/1/13 下午6:04, zhong jiang wrote:
>>
>> On 2021/1/12 10:55 上午, Ruan Shiyang wrote:
>>>
>>>
>>> On 2021/1/6 下午11:41, Jan Kara wrote:
>>>> On Thu 31-12-20 00:55:55, Shiyang Ruan wrote:
>>>>> The current memory_failure_dev_pagemap() can only handle 
>>>>> single-mapped
>>>>> dax page for fsdax mode.  The dax page could be mapped by multiple 
>>>>> files
>>>>> and offsets if we let reflink feature & fsdax mode work together.  
>>>>> So,
>>>>> we refactor current implementation to support handle memory 
>>>>> failure on
>>>>> each file and offset.
>>>>>
>>>>> Signed-off-by: Shiyang Ruan <ruansy.fnst@...fujitsu.com>
>>>>
>>>> Overall this looks OK to me, a few comments below.
>>>>
>>>>> ---
>>>>>   fs/dax.c            | 21 +++++++++++
>>>>>   include/linux/dax.h |  1 +
>>>>>   include/linux/mm.h  |  9 +++++
>>>>>   mm/memory-failure.c | 91 
>>>>> ++++++++++++++++++++++++++++++++++-----------
>>>>>   4 files changed, 100 insertions(+), 22 deletions(-)
>>>
>>> ...
>>>
>>>>>   @@ -345,9 +348,12 @@ static void add_to_kill(struct task_struct 
>>>>> *tsk, struct page *p,
>>>>>       }
>>>>>         tk->addr = page_address_in_vma(p, vma);
>>>>> -    if (is_zone_device_page(p))
>>>>> -        tk->size_shift = dev_pagemap_mapping_shift(p, vma);
>>>>> -    else
>>>>> +    if (is_zone_device_page(p)) {
>>>>> +        if (is_device_fsdax_page(p))
>>>>> +            tk->addr = vma->vm_start +
>>>>> +                    ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
>>>>
>>>> It seems strange to use 'pgoff' for dax pages and not for any other 
>>>> page.
>>>> Why? I'd rather pass correct pgoff from all callers of 
>>>> add_to_kill() and
>>>> avoid this special casing...
>>>
>>> Because one fsdax page can be shared by multiple pgoffs.  I have to 
>>> pass each pgoff in each iteration to calculate the address in vma 
>>> (for tk->addr).  Other kinds of pages don't need this. They can get 
>>> their unique address by calling "page_address_in_vma()".
>>>
>> IMO,   an fsdax page can be shared by multiple files rather than 
>> multiple pgoffs if fs query support reflink.   Because an page only 
>> located in an mapping(page->mapping is exclusive), hence it  only has 
>> an pgoff or index pointing at the node.
>>
>>   or  I miss something for the feature ?  thanks,
>
> Yes, a fsdax page is shared by multiple files because of reflink. I 
> think my description of 'pgoff' here is not correct.  This 'pgoff' 
> means the offset within the a file.  (We use rmap to find out all the 
> sharing files and their offsets.)  So, I said that "can be shared by 
> multiple pgoffs".  It's my bad.
>
> I think I should name it another word to avoid misunderstandings.
>
IMO,  All the sharing files should be the same offset to share the fsdax 
page.  why not that ?  As you has said,  a shared fadax page should be 
inserted to different mapping files.  but page->index and page->mapping 
is exclusive.  hence an page only should be placed in an mapping tree.

And In the current patch,  we failed to found out that all process use 
the fsdax page shared by multiple files and kill them.


Thanks,

> -- 
> Thanks,
> Ruan Shiyang.
>
>>
>>> So, I added this fsdax case here.  This patchset only implemented 
>>> the fsdax case, other cases also need to be added here if to be 
>>> implemented.
>>>
>>>
>>> -- 
>>> Thanks,
>>> Ruan Shiyang.
>>>
>>>>
>>>>> +        tk->size_shift = dev_pagemap_mapping_shift(p, vma, 
>>>>> tk->addr);
>>>>> +    } else
>>>>>           tk->size_shift = page_shift(compound_head(p));
>>>>>         /*
>>>>> @@ -495,7 +501,7 @@ static void collect_procs_anon(struct page 
>>>>> *page, struct list_head *to_kill,
>>>>>               if (!page_mapped_in_vma(page, vma))
>>>>>                   continue;
>>>>>               if (vma->vm_mm == t->mm)
>>>>> -                add_to_kill(t, page, vma, to_kill);
>>>>> +                add_to_kill(t, page, NULL, 0, vma, to_kill);
>>>>>           }
>>>>>       }
>>>>>       read_unlock(&tasklist_lock);
>>>>> @@ -505,24 +511,19 @@ static void collect_procs_anon(struct page 
>>>>> *page, struct list_head *to_kill,
>>>>>   /*
>>>>>    * Collect processes when the error hit a file mapped page.
>>>>>    */
>>>>> -static void collect_procs_file(struct page *page, struct 
>>>>> list_head *to_kill,
>>>>> -                int force_early)
>>>>> +static void collect_procs_file(struct page *page, struct 
>>>>> address_space *mapping,
>>>>> +        pgoff_t pgoff, struct list_head *to_kill, int force_early)
>>>>>   {
>>>>>       struct vm_area_struct *vma;
>>>>>       struct task_struct *tsk;
>>>>> -    struct address_space *mapping = page->mapping;
>>>>> -    pgoff_t pgoff;
>>>>>         i_mmap_lock_read(mapping);
>>>>>       read_lock(&tasklist_lock);
>>>>> -    pgoff = page_to_pgoff(page);
>>>>>       for_each_process(tsk) {
>>>>>           struct task_struct *t = task_early_kill(tsk, force_early);
>>>>> -
>>>>>           if (!t)
>>>>>               continue;
>>>>> -        vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff,
>>>>> -                      pgoff) {
>>>>> +        vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, 
>>>>> pgoff) {
>>>>>               /*
>>>>>                * Send early kill signal to tasks where a vma covers
>>>>>                * the page but the corrupted page is not necessarily
>>>>> @@ -531,7 +532,7 @@ static void collect_procs_file(struct page 
>>>>> *page, struct list_head *to_kill,
>>>>>                * to be informed of all such data corruptions.
>>>>>                */
>>>>>               if (vma->vm_mm == t->mm)
>>>>> -                add_to_kill(t, page, vma, to_kill);
>>>>> +                add_to_kill(t, page, mapping, pgoff, vma, to_kill);
>>>>>           }
>>>>>       }
>>>>>       read_unlock(&tasklist_lock);
>>>>> @@ -550,7 +551,8 @@ static void collect_procs(struct page *page, 
>>>>> struct list_head *tokill,
>>>>>       if (PageAnon(page))
>>>>>           collect_procs_anon(page, tokill, force_early);
>>>>>       else
>>>>> -        collect_procs_file(page, tokill, force_early);
>>>>> +        collect_procs_file(page, page->mapping, page_to_pgoff(page),
>>>>
>>>> Why not use page_mapping() helper here? It would be safer for THPs 
>>>> if they
>>>> ever get here...
>>>>
>>>>                                 Honza
>>>>
>>>
>>
>>
>

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