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From:   Michal Hocko <mhocko@kernel.org>
To:     <linux-mm@kvack.org>
Cc:     Dave Chinner <david@fromorbit.com>, Neil Brown <neilb@suse.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Hellwig <hch@infradead.org>,
        Uladzislau Rezki <urezki@gmail.com>,
        <linux-fsdevel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Ilya Dryomov <idryomov@gmail.com>,
        Jeff Layton <jlayton@kernel.org>,
        Michal Hocko <mhocko@suse.com>
Subject: [PATCH 2/4] mm/vmalloc: add support for __GFP_NOFAIL
Date:   Mon, 25 Oct 2021 17:02:21 +0200
Message-Id: <20211025150223.13621-3-mhocko@kernel.org>
In-Reply-To: <20211025150223.13621-1-mhocko@kernel.org>
References: <20211025150223.13621-1-mhocko@kernel.org>
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From: Michal Hocko <mhocko@suse.com>

Dave Chinner has mentioned that some of the xfs code would benefit from
kvmalloc support for __GFP_NOFAIL because they have allocations that
cannot fail and they do not fit into a single page.

The larg part of the vmalloc implementation already complies with the
given gfp flags so there is no work for those to be done. The area
and page table allocations are an exception to that. Implement a retry
loop for those.

Add a short sleep before retrying. 1 jiffy is a completely random
timeout. Ideally the retry would wait for an explicit event - e.g.
a change to the vmalloc space change if the failure was caused by
the space fragmentation or depletion. But there are multiple different
reasons to retry and this could become much more complex. Keep the retry
simple for now and just sleep to prevent from hogging CPUs.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 mm/vmalloc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index c6cc77d2f366..602649919a9d 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2941,8 +2941,12 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 	else if ((gfp_mask & (__GFP_FS | __GFP_IO)) == 0)
 		flags = memalloc_noio_save();
 
-	ret = vmap_pages_range(addr, addr + size, prot, area->pages,
+	do {
+		ret = vmap_pages_range(addr, addr + size, prot, area->pages,
 			page_shift);
+		if (ret < 0)
+			schedule_timeout_uninterruptible(1);
+	} while ((gfp_mask & __GFP_NOFAIL) && (ret < 0));
 
 	if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
 		memalloc_nofs_restore(flags);
@@ -3032,6 +3036,10 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 		warn_alloc(gfp_mask, NULL,
 			"vmalloc error: size %lu, vm_struct allocation failed",
 			real_size);
+		if (gfp_mask & __GFP_NOFAIL) {
+			schedule_timeout_uninterruptible(1);
+			goto again;
+		}
 		goto fail;
 	}
 
-- 
2.30.2