linux-ext4 - [PATCH 5/6] XFS: remove congestion_wait() loop from kmem

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Date:   Fri, 17 Sep 2021 12:56:57 +1000
From:   NeilBrown <neilb@...e.de>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.com>,
        ". Dave Chinner" <david@...morbit.com>,
        Jonathan Corbet <corbet@....net>
Cc:     linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: [PATCH 5/6] XFS: remove congestion_wait() loop from kmem_alloc()

Documentation commment in gfp.h discourages indefinite retry loops on
ENOMEM and says of __GFP_NOFAIL that it

    is definitely preferable to use the flag rather than opencode
    endless loop around allocator.

So remove the loop, instead specifying __GFP_NOFAIL if KM_MAYFAIL was
not given.

As we no longer have the opportunity to report a warning after some
failures, clear __GFP_NOWARN so that the default warning (rate-limited
to 1 ever 10 seconds) will be reported instead.

Signed-off-by: NeilBrown <neilb@...e.de>
---
 fs/xfs/kmem.c |   19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
index 6f49bf39183c..575a58e61391 100644
--- a/fs/xfs/kmem.c
+++ b/fs/xfs/kmem.c
@@ -11,21 +11,14 @@
 void *
 kmem_alloc(size_t size, xfs_km_flags_t flags)
 {
-	int	retries = 0;
 	gfp_t	lflags = kmem_flags_convert(flags);
-	void	*ptr;
 
 	trace_kmem_alloc(size, flags, _RET_IP_);
 
-	do {
-		ptr = kmalloc(size, lflags);
-		if (ptr || (flags & KM_MAYFAIL))
-			return ptr;
-		if (!(++retries % 100))
-			xfs_err(NULL,
-	"%s(%u) possible memory allocation deadlock size %u in %s (mode:0x%x)",
-				current->comm, current->pid,
-				(unsigned int)size, __func__, lflags);
-		congestion_wait(BLK_RW_ASYNC, HZ/50);
-	} while (1);
+	if (!(flags & KM_MAYFAIL)) {
+		lflags |= __GFP_NOFAIL;
+		lflags &= ~__GFP_NOWARN;
+	}
+
+	return kmalloc(size, lflags);
 }