Re: [PATCH 04/10] mm, fsdax: Refactor memory-failure handler for dax mapping

[Ruan Shiyang]

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@xxxxxxxxxxxxxx>
>
> 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()".

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