On Mon 09-01-17 15:08:27, Vlastimil Babka wrote:

On 01/06/2017 03:11 PM, Michal Hocko wrote:

quoted

From: Michal Hocko <mhocko@suse.com>

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@suse.com>

Not a xfs expert, but seems correct.

Acked-by: Vlastimil Babka <redacted>

Thanks!

Nit below:

quoted

---
 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

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