[Intel-gfx] [PATCH v4 1/2] shmem: Support for registration of driver/file owner specific ops

[Daniel Vetter]

On Fri, Apr 15, 2016 at 05:09:24PM +0100, Chris Wilson wrote:
> On Mon, Apr 04, 2016 at 02:18:10PM +0100, Chris Wilson wrote:
> > From: Akash Goel <akash.goel at intel.com>
> > 
> > This provides support for the drivers or shmem file owners to register
> > a set of callbacks, which can be invoked from the address space
> > operations methods implemented by shmem.  This allow the file owners to
> > hook into the shmem address space operations to do some extra/custom
> > operations in addition to the default ones.
> > 
> > The private_data field of address_space struct is used to store the
> > pointer to driver specific ops.  Currently only one ops field is defined,
> > which is migratepage, but can be extended on an as-needed basis.
> > 
> > The need for driver specific operations arises since some of the
> > operations (like migratepage) may not be handled completely within shmem,
> > so as to be effective, and would need some driver specific handling also.
> > Specifically, i915.ko would like to participate in migratepage().
> > i915.ko uses shmemfs to provide swappable backing storage for its user
> > objects, but when those objects are in use by the GPU it must pin the
> > entire object until the GPU is idle.  As a result, large chunks of memory
> > can be arbitrarily withdrawn from page migration, resulting in premature
> > out-of-memory due to fragmentation.  However, if i915.ko can receive the
> > migratepage() request, it can then flush the object from the GPU, remove
> > its pin and thus enable the migration.
> > 
> > Since gfx allocations are one of the major consumer of system memory, its
> > imperative to have such a mechanism to effectively deal with
> > fragmentation.  And therefore the need for such a provision for initiating
> > driver specific actions during address space operations.
> > 
> > Cc: Hugh Dickins <hughd at google.com>
> > Cc: linux-mm at kvack.org
> > Cc: linux-kernel at vger.linux.org
> > Signed-off-by: Sourab Gupta <sourab.gupta at intel.com>
> > Signed-off-by: Akash Goel <akash.goel at intel.com>
> > Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> 
> Ping?

This addresses a long-standing issue we have in i915 gem of essentially
pinning way to much memory as unmoveable. Would be nice to get this
merged. It also does seem to fix some real-world issues we're seeing
(linked from the i915 patch).

Can I have acks/reviews from -mm folks to get this in through drm trees
please?

Thanks, Daniel

> 
> > ---
> >  include/linux/shmem_fs.h | 17 +++++++++++++++++
> >  mm/shmem.c               | 17 ++++++++++++++++-
> >  2 files changed, 33 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> > index 4d4780c00d34..d7925b66c240 100644
> > --- a/include/linux/shmem_fs.h
> > +++ b/include/linux/shmem_fs.h
> > @@ -34,11 +34,28 @@ struct shmem_sb_info {
> >  	struct mempolicy *mpol;     /* default memory policy for mappings */
> >  };
> >  
> > +struct shmem_dev_info {
> > +	void *dev_private_data;
> > +	int (*dev_migratepage)(struct address_space *mapping,
> > +			       struct page *newpage, struct page *page,
> > +			       enum migrate_mode mode, void *dev_priv_data);
> > +};
> > +
> >  static inline struct shmem_inode_info *SHMEM_I(struct inode *inode)
> >  {
> >  	return container_of(inode, struct shmem_inode_info, vfs_inode);
> >  }
> >  
> > +static inline int shmem_set_device_ops(struct address_space *mapping,
> > +				       struct shmem_dev_info *info)
> > +{
> > +	if (mapping->private_data != NULL)
> > +		return -EEXIST;
> > +
> > +	mapping->private_data = info;
> > +	return 0;
> > +}
> > +
> >  /*
> >   * Functions in mm/shmem.c called directly from elsewhere:
> >   */
> > diff --git a/mm/shmem.c b/mm/shmem.c
> > index 9428c51ab2d6..6ed953193883 100644
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -947,6 +947,21 @@ redirty:
> >  	return 0;
> >  }
> >  
> > +#ifdef CONFIG_MIGRATION
> > +static int shmem_migratepage(struct address_space *mapping,
> > +			     struct page *newpage, struct page *page,
> > +			     enum migrate_mode mode)
> > +{
> > +	struct shmem_dev_info *dev_info = mapping->private_data;
> > +
> > +	if (dev_info && dev_info->dev_migratepage)
> > +		return dev_info->dev_migratepage(mapping, newpage, page,
> > +				mode, dev_info->dev_private_data);
> > +
> > +	return migrate_page(mapping, newpage, page, mode);
> > +}
> > +#endif
> > +
> >  #ifdef CONFIG_NUMA
> >  #ifdef CONFIG_TMPFS
> >  static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
> > @@ -3161,7 +3176,7 @@ static const struct address_space_operations shmem_aops = {
> >  	.write_end	= shmem_write_end,
> >  #endif
> >  #ifdef CONFIG_MIGRATION
> > -	.migratepage	= migrate_page,
> > +	.migratepage	= shmem_migratepage,
> >  #endif
> >  	.error_remove_page = generic_error_remove_page,
> >  };
> 
> -- 
> Chris Wilson, Intel Open Source Technology Centre
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch