9p, afs, ceph, nfs: Use current_is_kswapd() rather than gfpflags_allow_blocking()

In 9p, afs ceph, and nfs, gfpflags_allow_blocking() (which wraps a
test for __GFP_DIRECT_RECLAIM being set) is used to determine if
->releasepage() should wait for the completion of a DIO write to fscache
with something like:

	if (folio_test_fscache(folio)) {
		if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
			return false;
		folio_wait_fscache(folio);
	}

Instead, current_is_kswapd() should be used instead.

Note that this is based on a patch originally by Zhaoyang Huang[1].  In
addition to extending it to the other network filesystems and putting it on
top of my fscache rewrite, it also needs to include linux/swap.h in a bunch
of places.  Can current_is_kswapd() be moved to linux/mm.h?

Changes
=======
ver #5:
 - Dropping the changes for cifs.

Originally-signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
Co-developed-by: David Howells <dhowells@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Steve French <smfrench@gmail.com>
cc: Trond Myklebust <trond.myklebust@hammerspace.com>
cc: linux-cachefs@redhat.com
cc: v9fs-developer@lists.sourceforge.net
cc: linux-afs@lists.infradead.org
cc: ceph-devel@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: linux-nfs@vger.kernel.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/1638952658-20285-1-git-send-email-huangzhaoyang@gmail.com/ [1]
Link: https://lore.kernel.org/r/164021590773.640689.16777975200823659231.stgit@warthog.procyon.org.uk/ # v4

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/nfs/fscache.h b/fs/nfs/fscache.h
index e0220fc40366..25a5c0f82392 100644
--- a/fs/nfs/fscache.h
+++ b/fs/nfs/fscache.h
@@ -8,6 +8,7 @@
 #ifndef _NFS_FSCACHE_H
 #define _NFS_FSCACHE_H
 
+#include <linux/swap.h>
 #include <linux/nfs_fs.h>
 #include <linux/nfs_mount.h>
 #include <linux/nfs4_mount.h>
@@ -52,7 +53,7 @@ extern void __nfs_readpage_to_fscache(struct inode *, struct page *);
 static inline int nfs_fscache_release_page(struct page *page, gfp_t gfp)
 {
 	if (PageFsCache(page)) {
-		if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
+		if (current_is_kswapd() || !(gfp & __GFP_FS))
 			return false;
 		wait_on_page_fscache(page);
 		fscache_note_page_release(nfs_i_fscache(page->mapping->host));