Re: [PATCH 4/8] xfs: use memalloc_nofs_{save,restore} instead of memalloc_noio*

[Michal Hocko]

On Mon 09-01-17 15:08:27, Vlastimil Babka wrote:
> On 01/06/2017 03:11 PM, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@xxxxxxxx>
> > 
> > kmem_zalloc_large and _xfs_buf_map_pages use memalloc_noio_{save,restore}
> > API to prevent from reclaim recursion into the fs because vmalloc can
> > invoke unconditional GFP_KERNEL allocations and these functions might be
> > called from the NOFS contexts. The memalloc_noio_save will enforce
> > GFP_NOIO context which is even weaker than GFP_NOFS and that seems to be
> > unnecessary. Let's use memalloc_nofs_{save,restore} instead as it should
> > provide exactly what we need here - implicit GFP_NOFS context.
> > 
> > Changes since v1
> > - s@memalloc_noio_restore@memalloc_nofs_restore@ in _xfs_buf_map_pages
> >   as per Brian Foster
> > 
> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> 
> Not a xfs expert, but seems correct.
> 
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

Thanks!

> 
> Nit below:
> 
> > ---
> >  fs/xfs/kmem.c    | 10 +++++-----
> >  fs/xfs/xfs_buf.c |  8 ++++----
> >  2 files changed, 9 insertions(+), 9 deletions(-)
> > 
> > diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> > index a76a05dae96b..d69ed5e76621 100644
> > --- a/fs/xfs/kmem.c
> > +++ b/fs/xfs/kmem.c
> > @@ -65,7 +65,7 @@ kmem_alloc(size_t size, xfs_km_flags_t flags)
> >  void *
> >  kmem_zalloc_large(size_t size, xfs_km_flags_t flags)
> >  {
> > -	unsigned noio_flag = 0;
> > +	unsigned nofs_flag = 0;
> >  	void	*ptr;
> >  	gfp_t	lflags;
> >  
> > @@ -80,14 +80,14 @@ kmem_zalloc_large(size_t size, xfs_km_flags_t flags)
> >  	 * context via PF_MEMALLOC_NOIO to prevent memory reclaim re-entering
> >  	 * the filesystem here and potentially deadlocking.
> 
> The comment above is now largely obsolete, or minimally should be
> changed to PF_MEMALLOC_NOFS?
---
diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
index d69ed5e76621..0c9f94f41b6c 100644
--- a/fs/xfs/kmem.c
+++ b/fs/xfs/kmem.c
@@ -77,7 +77,7 @@ kmem_zalloc_large(size_t size, xfs_km_flags_t flags)
 	 * __vmalloc() will allocate data pages and auxillary structures (e.g.
 	 * pagetables) with GFP_KERNEL, yet we may be under GFP_NOFS context
 	 * here. Hence we need to tell memory reclaim that we are in such a
-	 * context via PF_MEMALLOC_NOIO to prevent memory reclaim re-entering
+	 * context via PF_MEMALLOC_NOFS to prevent memory reclaim re-entering
 	 * the filesystem here and potentially deadlocking.
 	 */
 	if (flags & KM_NOFS)

I will fold it into the original patch.

Thanks!
-- 
Michal Hocko
SUSE Labs