Re: [PATCH v3] mm: add replace_page_cache_page() function

[Minchan Kim]

On Fri, Jan 14, 2011 at 10:00:37AM +0900, Daisuke Nishimura wrote:
> On Thu, 13 Jan 2011 14:35:09 +0100
> Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> 
> > > Seems nicer. But you didn't fixed the caller of prepare_migraton()
> > > in mm/migrate.c (I think this is the only caller..)
> > > 
> > > please modify it, too.
> > 
> > Right you are.  Thanks for the review.
> > 
> > Updated patch attached.
> > 
> > Thanks,
> > Miklos
> > ---
> > 
> > 
> > From: Miklos Szeredi <mszeredi@xxxxxxx>
> > Subject: mm: add replace_page_cache_page() function
> > 
> > This function basically does:
> > 
> >      remove_from_page_cache(old);
> >      page_cache_release(old);
> >      add_to_page_cache_locked(new);
> > 
> > Except it does this atomically, so there's no possibility for the
> > "add" to fail because of a race.
> > 
> > This is used by fuse to move pages into the page cache.
> > 
> > Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
> > ---
> >  fs/fuse/dev.c              |   10 ++----
> >  include/linux/memcontrol.h |    4 +-
> >  include/linux/pagemap.h    |    1 
> >  mm/filemap.c               |   65 +++++++++++++++++++++++++++++++++++++++++++++
> >  mm/memcontrol.c            |    4 +-
> >  mm/migrate.c               |    2 -
> >  6 files changed, 75 insertions(+), 11 deletions(-)
> > 
> > Index: linux-2.6/mm/filemap.c
> > ===================================================================
> > --- linux-2.6.orig/mm/filemap.c	2011-01-12 15:28:56.000000000 +0100
> > +++ linux-2.6/mm/filemap.c	2011-01-13 13:37:41.000000000 +0100
> > @@ -387,6 +387,71 @@ int filemap_write_and_wait_range(struct
> >  EXPORT_SYMBOL(filemap_write_and_wait_range);
> >  
> >  /**
> > + * replace_page_cache_page - replace a pagecache page with a new one
> > + * @old:	page to be replaced
> > + * @new:	page to replace with
> > + * @gfp_mask:	allocation mode
> > + *
> > + * This function replaces a page in the pagecache with a new one.  On
> > + * success it acquires the pagecache reference for the new page and
> > + * drops it for the old page.  Both the old and new pages must be
> > + * locked.  This function does not add the new page to the LRU, the
> > + * caller must do that.
> > + *
> > + * The remove + add is atomic.  The only way this function can fail is
> > + * memory allocation failure.
> > + */
> > +int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
> > +{
> > +	int error;
> > +	struct mem_cgroup *memcg = NULL;
> > +
> > +	VM_BUG_ON(!PageLocked(old));
> > +	VM_BUG_ON(!PageLocked(new));
> > +	VM_BUG_ON(new->mapping);
> > +
> > +	/*
> > +	 * This is not page migration, but prepare_migration and
> > +	 * end_migration does enough work for charge replacement.
> > +	 *
> > +	 * In the longer term we probably want a specialized function
> > +	 * for moving the charge from old to new in a more efficient
> > +	 * manner.
> > +	 */
> > +	error = mem_cgroup_prepare_migration(old, new, &memcg, gfp_mask);
> > +	if (error)
> > +		return error;
> > +
> > +	error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
> > +	if (!error) {
> > +		struct address_space *mapping = old->mapping;
> > +		pgoff_t offset = old->index;
> > +
> > +		page_cache_get(new);
> > +		new->mapping = mapping;
> > +		new->index = offset;
> > +
> > +		spin_lock_irq(&mapping->tree_lock);
> > +		__remove_from_page_cache(old);
> > +		error = radix_tree_insert(&mapping->page_tree, offset, new);
> > +		BUG_ON(error);
> > +		mapping->nrpages++;
> > +		__inc_zone_page_state(new, NR_FILE_PAGES);
> > +		if (PageSwapBacked(new))
> > +			__inc_zone_page_state(new, NR_SHMEM);
> > +		spin_unlock_irq(&mapping->tree_lock);
> > +		radix_tree_preload_end();
> > +		page_cache_release(old);
> > +		mem_cgroup_end_migration(memcg, old, new, true);
> > +	} else {
> > +		mem_cgroup_end_migration(memcg, old, new, false);
> > +	}
> > +
> > +	return error;
> > +}
> > +EXPORT_SYMBOL_GPL(replace_page_cache_page);
> > +
> > +/**
> >   * add_to_page_cache_locked - add a locked page to the pagecache
> >   * @page:	page to add
> >   * @mapping:	the page's address_space
> > Index: linux-2.6/include/linux/pagemap.h
> > ===================================================================
> > --- linux-2.6.orig/include/linux/pagemap.h	2011-01-12 15:28:56.000000000 +0100
> > +++ linux-2.6/include/linux/pagemap.h	2011-01-13 13:37:41.000000000 +0100
> > @@ -457,6 +457,7 @@ int add_to_page_cache_lru(struct page *p
> >  				pgoff_t index, gfp_t gfp_mask);
> >  extern void remove_from_page_cache(struct page *page);
> >  extern void __remove_from_page_cache(struct page *page);
> > +int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask);
> >  
> >  /*
> >   * Like add_to_page_cache_locked, but used to add newly allocated pages:
> > Index: linux-2.6/fs/fuse/dev.c
> > ===================================================================
> > --- linux-2.6.orig/fs/fuse/dev.c	2011-01-12 15:28:56.000000000 +0100
> > +++ linux-2.6/fs/fuse/dev.c	2011-01-13 13:37:41.000000000 +0100
> > @@ -737,14 +737,12 @@ static int fuse_try_move_page(struct fus
> >  	if (WARN_ON(PageMlocked(oldpage)))
> >  		goto out_fallback_unlock;
> >  
> > -	remove_from_page_cache(oldpage);
> > -	page_cache_release(oldpage);
> > -
> > -	err = add_to_page_cache_locked(newpage, mapping, index, GFP_KERNEL);
> > +	err = replace_page_cache_page(oldpage, newpage, GFP_KERNEL);
> >  	if (err) {
> > -		printk(KERN_WARNING "fuse_try_move_page: failed to add page");
> > -		goto out_fallback_unlock;
> > +		unlock_page(newpage);
> > +		return err;
> >  	}
> > +
> >  	page_cache_get(newpage);
> >  
> >  	if (!(buf->flags & PIPE_BUF_FLAG_LRU))
> > Index: linux-2.6/include/linux/memcontrol.h
> > ===================================================================
> > --- linux-2.6.orig/include/linux/memcontrol.h	2011-01-13 13:37:40.000000000 +0100
> > +++ linux-2.6/include/linux/memcontrol.h	2011-01-13 13:37:41.000000000 +0100
> > @@ -91,7 +91,7 @@ extern struct cgroup_subsys_state *mem_c
> >  
> >  extern int
> >  mem_cgroup_prepare_migration(struct page *page,
> > -	struct page *newpage, struct mem_cgroup **ptr);
> > +	struct page *newpage, struct mem_cgroup **ptr, gfp_t gfp_mask);
> >  extern void mem_cgroup_end_migration(struct mem_cgroup *mem,
> >  	struct page *oldpage, struct page *newpage, bool migration_ok);
> >  
> > @@ -225,7 +225,7 @@ static inline struct cgroup_subsys_state
> >  
> >  static inline int
> >  mem_cgroup_prepare_migration(struct page *page, struct page *newpage,
> > -	struct mem_cgroup **ptr)
> > +	struct mem_cgroup **ptr, gfp_t gfp_mask)
> >  {
> >  	return 0;
> >  }
> > Index: linux-2.6/mm/memcontrol.c
> > ===================================================================
> > --- linux-2.6.orig/mm/memcontrol.c	2011-01-13 13:37:40.000000000 +0100
> > +++ linux-2.6/mm/memcontrol.c	2011-01-13 13:37:41.000000000 +0100
> > @@ -2767,7 +2767,7 @@ static inline int mem_cgroup_move_swap_a
> >   * page belongs to.
> >   */
> >  int mem_cgroup_prepare_migration(struct page *page,
> > -	struct page *newpage, struct mem_cgroup **ptr)
> > +	struct page *newpage, struct mem_cgroup **ptr, gfp_t gfp_mask)
> >  {
> >  	struct page_cgroup *pc;
> >  	struct mem_cgroup *mem = NULL;
> > @@ -2823,7 +2823,7 @@ int mem_cgroup_prepare_migration(struct
> >  		return 0;
> >  
> >  	*ptr = mem;
> > -	ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, ptr, false);
> > +	ret = __mem_cgroup_try_charge(NULL, gfp_mask, ptr, false);
> >  	css_put(&mem->css);/* drop extra refcnt */
> >  	if (ret || *ptr == NULL) {
> >  		if (PageAnon(page)) {
> > Index: linux-2.6/mm/migrate.c
> > ===================================================================
> > --- linux-2.6.orig/mm/migrate.c	2011-01-13 13:37:40.000000000 +0100
> > +++ linux-2.6/mm/migrate.c	2011-01-13 13:38:55.000000000 +0100
> > @@ -657,7 +657,7 @@ static int unmap_and_move(new_page_t get
> >  	}
> >  
> >  	/* charge against new page */
> > -	charge = mem_cgroup_prepare_migration(page, newpage, &mem);
> > +	charge = mem_cgroup_prepare_migration(page, newpage, &mem, GFP_KERNEL);
> >  	if (charge == -ENOMEM) {
> >  		rc = -ENOMEM;
> >  		goto unlock;
> This patch looks good and I want to ack, but this patch can conflict with patches
> in https://lkml.org/lkml/2011/1/11/10 and https://lkml.org/lkml/2011/1/11/65.
> So I think you'd better coordinate with Minchan.

And it can conflict with https://patchwork.kernel.org/patch/470311/
I am not sure Andrew accept it easily although many mm guys already acked and reviewed it.
So I hope patch ordering is following as after mmotm release

1. https://lkml.org/lkml/2011/1/11/10 and https://lkml.org/lkml/2011/1/11/65
2. your patch
3. https://patchwork.kernel.org/patch/470311/

If you have a problem, please let me know it.

> 
> Thanks,
> Daisuke Nishimura.

-- 
Kind regards,
Minchan Kim
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