Re: [PATCH 07/10] mm: page_alloc: Rename __GFP_WAIT to __GFP_RECLAIM

[Mel Gorman <mgorman@techsingularity.net>]

On Fri, Aug 21, 2015 at 04:20:52PM +0200, Vlastimil Babka wrote:
> On 08/12/2015 12:45 PM, Mel Gorman wrote:
> >__GFP_WAIT was used to signal that the caller was in atomic context and
> >could not sleep.  Now it is possible to distinguish between true atomic
> >context and callers that are not willing to sleep. The latter should clear
> >__GFP_DIRECT_RECLAIM so kswapd will still wake. As clearing __GFP_WAIT
> >behaves differently, there is a risk that people will clear the wrong
> >flags. This patch renames __GFP_WAIT to __GFP_RECLAIM to clearly indicate
> >what it does -- setting it allows all reclaim activity, clearing them
> >prevents it.
> >
> >Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> 
> ...
> 
> >diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
> >index c097909c589c..1d2046e68808 100644
> >--- a/drivers/block/drbd/drbd_receiver.c
> >+++ b/drivers/block/drbd/drbd_receiver.c
> >@@ -357,7 +357,7 @@ drbd_alloc_peer_req(struct drbd_peer_device *peer_device, u64 id, sector_t secto
> >  	}
> >
> >  	if (has_payload && data_size) {
> >-		page = drbd_alloc_pages(peer_device, nr_pages, (gfp_mask & __GFP_WAIT));
> >+		page = drbd_alloc_pages(peer_device, nr_pages, (gfp_mask & __GFP_RECLAIM));
> 

Yeah.

> I think here it should test only for direct reclaim (via the helper) and
> thus moved to patch 06?
> 
> >--- a/drivers/gpu/drm/i915/i915_gem.c
> >+++ b/drivers/gpu/drm/i915/i915_gem.c
> >@@ -2226,7 +2226,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
> >  	mapping = file_inode(obj->base.filp)->i_mapping;
> >  	gfp = mapping_gfp_mask(mapping);
> >  	gfp |= __GFP_NORETRY | __GFP_NOWARN;
> >-	gfp &= ~(__GFP_IO | __GFP_WAIT);
> >+	gfp &= ~(__GFP_IO | __GFP_RECLAIM);
> 
> Why clear the kswapd reclaim here?
> 

Because in patch 6, it was using __GFP_NO_KSWAPD so it's in line with
the expected behaviour of the code.

> >diff --git a/drivers/staging/lustre/include/linux/libcfs/libcfs_private.h b/drivers/staging/lustre/include/linux/libcfs/libcfs_private.h
> >index ed37d26eb20d..393270436a4b 100644
> >--- a/drivers/staging/lustre/include/linux/libcfs/libcfs_private.h
> >+++ b/drivers/staging/lustre/include/linux/libcfs/libcfs_private.h
> >@@ -113,7 +113,7 @@ do {						\
> >  do {									    \
> >  	LASSERT(!in_interrupt() ||					    \
> >  		((size) <= LIBCFS_VMALLOC_SIZE &&			    \
> >-		 ((mask) & __GFP_WAIT) == 0));				    \
> >+		 ((mask) & __GFP_RECLAIM) == 0));			    \
> >  } while (0)
> 
> This should test only __GFP_DIRECT_RECLAIM?
> 

Yes and it should be in patch 6.

> >  #define LIBCFS_ALLOC_POST(ptr, size)					    \
> >diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> >index 35660da77921..92e284d0362e 100644
> >--- a/fs/btrfs/extent_io.c
> >+++ b/fs/btrfs/extent_io.c
> >@@ -718,7 +718,7 @@ int clear_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
> >  	if (start > end)
> >  		goto out;
> >  	spin_unlock(&tree->lock);
> >-	if (mask & __GFP_WAIT)
> >+	if (mask & __GFP_RECLAIM)
> >  		cond_resched();
> >  	goto again;
> >  }
> >@@ -1028,7 +1028,7 @@ __set_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
> >  	if (start > end)
> >  		goto out;
> >  	spin_unlock(&tree->lock);
> >-	if (mask & __GFP_WAIT)
> >+	if (mask & __GFP_RECLAIM)
> >  		cond_resched();
> >  	goto again;
> >  }
> >@@ -1253,7 +1253,7 @@ int convert_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
> >  	if (start > end)
> >  		goto out;
> >  	spin_unlock(&tree->lock);
> >-	if (mask & __GFP_WAIT)
> >+	if (mask & __GFP_RECLAIM)
> >  		cond_resched();
> >  	first_iteration = false;
> >  	goto again;
> 
> This too?
> 

Yes.

> >diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> >index dbd246a14e2f..e066f3afae73 100644
> >--- a/include/linux/gfp.h
> >+++ b/include/linux/gfp.h
> >@@ -104,7 +104,7 @@ struct vm_area_struct;
> >   * can be cleared when the reclaiming of pages would cause unnecessary
> >   * disruption.
> >   */
> >-#define __GFP_WAIT (__GFP_DIRECT_RECLAIM|__GFP_KSWAPD_RECLAIM)
> >+#define __GFP_RECLAIM (__GFP_DIRECT_RECLAIM|__GFP_KSWAPD_RECLAIM)
> >  #define __GFP_DIRECT_RECLAIM	((__force gfp_t)___GFP_DIRECT_RECLAIM) /* Caller can reclaim */
> >  #define __GFP_KSWAPD_RECLAIM	((__force gfp_t)___GFP_KSWAPD_RECLAIM) /* kswapd can wake */
> >
> >@@ -123,12 +123,12 @@ struct vm_area_struct;
> >   */
> >  #define GFP_ATOMIC	(__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM)
> >  #define GFP_NOWAIT	(__GFP_KSWAPD_RECLAIM)
> >-#define GFP_NOIO	(__GFP_WAIT)
> >-#define GFP_NOFS	(__GFP_WAIT | __GFP_IO)
> >-#define GFP_KERNEL	(__GFP_WAIT | __GFP_IO | __GFP_FS)
> >-#define GFP_TEMPORARY	(__GFP_WAIT | __GFP_IO | __GFP_FS | \
> >+#define GFP_NOIO	(__GFP_RECLAIM)
> >+#define GFP_NOFS	(__GFP_RECLAIM | __GFP_IO)
> >+#define GFP_KERNEL	(__GFP_RECLAIM | __GFP_IO | __GFP_FS)
> >+#define GFP_TEMPORARY	(__GFP_RECLAIM | __GFP_IO | __GFP_FS | \
> >  			 __GFP_RECLAIMABLE)
> >-#define GFP_USER	(__GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_HARDWALL)
> >+#define GFP_USER	(__GFP_RECLAIM | __GFP_IO | __GFP_FS | __GFP_HARDWALL)
> >  #define GFP_HIGHUSER	(GFP_USER | __GFP_HIGHMEM)
> >  #define GFP_HIGHUSER_MOVABLE	(GFP_HIGHUSER | __GFP_MOVABLE)
> >  #define GFP_IOFS	(__GFP_IO | __GFP_FS)
> 
> Hmm GFP_IOFS should maybe include __GFP_KSWAPD_RECLAIM? Although I wonder if
> it makes sense to use it like "... | GFP_IOFS" and not just as a mask "... &
> ~GFP_IOFS". Not including __GFP_KSWAPD_RECLAIM changes the former use, while
> including it changes the latter one.
> Maybe we should just remove it while at it? There's only a handful of users.
> mm/ uses it as a mask, and the rest is in staging/lustre and it's doing
> allocations like "__GFP_ZERO | GFP_IOFS" which looks like a mistake to me -
> what good is IO or FS without DIRECT_RECLAIM?
> 
> It's probably best we removed it or changed it to __GFP_IOFS. The form
> without underscores suggests usage as parameter to alloc functions and
> that's clearly wrong here.
> 

I updated GFP_IOFS to include the flag but kept its existance. A few
sites needed to be converted to (__GFP_IO | __GFP_FS) to still be
correct. It's now part of patch 6

> >diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> >index d8e2e3918ce2..4bee2392dbb2 100644
> >--- a/net/netlink/af_netlink.c
> >+++ b/net/netlink/af_netlink.c
> >@@ -2061,7 +2061,7 @@ int netlink_broadcast_filtered(struct sock *ssk, struct sk_buff *skb, u32 portid
> >  	consume_skb(info.skb2);
> >
> >  	if (info.delivered) {
> >-		if (info.congested && (allocation & __GFP_WAIT))
> >+		if (info.congested && (allocation & __GFP_RECLAIM))
> >  			yield();
> 
> Just direct reclaim?
> 

Yeah

> >  		return 0;
> >  	}
> >diff --git a/net/rxrpc/ar-connection.c b/net/rxrpc/ar-connection.c
> >index 6631f4f1e39b..b5cd65401a28 100644
> >--- a/net/rxrpc/ar-connection.c
> >+++ b/net/rxrpc/ar-connection.c
> >@@ -500,7 +500,7 @@ int rxrpc_connect_call(struct rxrpc_sock *rx,
> >  		if (bundle->num_conns >= 20) {
> >  			_debug("too many conns");
> >
> >-			if (!(gfp & __GFP_WAIT)) {
> >+			if (!(gfp & __GFP_RECLAIM)) {
> >  				_leave(" = -EAGAIN");
> >  				return -EAGAIN;
> >  			}
> 
> ditto?
> 

Yeah.

-- 
Mel Gorman
SUSE Labs

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