From: Chris Goldsworthy <cgoldswo@codeaurora.org>
To: akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-arm-msm@vger.kernel.org,
linux-kernel@vger.kernel.org, pratikp@codeaurora.org,
pdaly@codeaurora.org, sudraja@codeaurora.org,
iamjoonsoo.kim@lge.com, linux-arm-msm-owner@vger.kernel.org,
Chris Goldsworthy <cgoldswo@codeaurora.org>,
Vinayak Menon <vinmenon@codeaurora.org>
Subject: [PATCH v2] mm: cma: indefinitely retry allocations in cma_alloc
Date: Fri, 11 Sep 2020 19:17:04 +0000 [thread overview]
Message-ID: <010101747e9985ab-785157c3-24c9-4e62-ab39-133d7736c4e8-000000@us-west-2.amazonses.com> (raw)
In-Reply-To: <1599851809-4342-1-git-send-email-cgoldswo@codeaurora.org>
CMA allocations will fail if 'pinned' pages are in a CMA area, since we
cannot migrate pinned pages. The _refcount of a struct page being greater
than _mapcount for that page can cause pinning for anonymous pages. This
is because try_to_unmap(), which (1) is called in the CMA allocation path,
and (2) decrements both _refcount and _mapcount for a page, will stop
unmapping a page from VMAs once the _mapcount for a page reaches 0. This
implies that after try_to_unmap() has finished successfully for a page
where _recount > _mapcount, that _refcount will be greater than 0. Later
in the CMA allocation path in migrate_page_move_mapping(), we will have one
more reference count than intended for anonymous pages, meaning the
allocation will fail for that page.
One example of where _refcount can be greater than _mapcount for a page we
would not expect to be pinned is inside of copy_one_pte(), which is called
during a fork. For ptes for which pte_present(pte) == true, copy_one_pte()
will increment the _refcount field followed by the _mapcount field of a
page. If the process doing copy_one_pte() is context switched out after
incrementing _refcount but before incrementing _mapcount, then the page
will be temporarily pinned.
So, inside of cma_alloc(), instead of giving up when alloc_contig_range()
returns -EBUSY after having scanned a whole CMA-region bitmap, perform
retries indefinitely, with sleeps, to give the system an opportunity to
unpin any pinned pages.
Signed-off-by: Chris Goldsworthy <cgoldswo@codeaurora.org>
Co-developed-by: Vinayak Menon <vinmenon@codeaurora.org>
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
---
mm/cma.c | 25 +++++++++++++++++++++++--
1 file changed, 23 insertions(+), 2 deletions(-)
diff --git a/mm/cma.c b/mm/cma.c
index 7f415d7..90bb505 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -32,6 +32,7 @@
#include <linux/highmem.h>
#include <linux/io.h>
#include <linux/kmemleak.h>
+#include <linux/delay.h>
#include <trace/events/cma.h>
#include "cma.h"
@@ -442,8 +443,28 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
bitmap_maxno, start, bitmap_count, mask,
offset);
if (bitmap_no >= bitmap_maxno) {
- mutex_unlock(&cma->lock);
- break;
+ if (ret == -EBUSY) {
+ mutex_unlock(&cma->lock);
+
+ /*
+ * Page may be momentarily pinned by some other
+ * process which has been scheduled out, e.g.
+ * in exit path, during unmap call, or process
+ * fork and so cannot be freed there. Sleep
+ * for 100ms and retry the allocation.
+ */
+ start = 0;
+ ret = -ENOMEM;
+ msleep(100);
+ continue;
+ } else {
+ /*
+ * ret == -ENOMEM - all bits in cma->bitmap are
+ * set, so we break accordingly.
+ */
+ mutex_unlock(&cma->lock);
+ break;
+ }
}
bitmap_set(cma->bitmap, bitmap_no, bitmap_count);
/*
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project
next prev parent reply other threads:[~2020-09-11 19:17 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <06489716814387e7f147cf53d1b185a8@codeaurora.org>
2020-09-11 19:17 ` [PATCH v2] cma_alloc(), indefinitely retry allocations for -EBUSY failures Chris Goldsworthy
[not found] ` <1599851809-4342-1-git-send-email-cgoldswo@codeaurora.org>
2020-09-11 19:17 ` Chris Goldsworthy [this message]
[not found] ` <010101747e998731-e49f209f-8232-4496-a9fc-2465334e70d7-000000@us-west-2.amazonses.com>
2020-09-14 9:31 ` [PATCH v2] mm: cma: indefinitely retry allocations in cma_alloc David Hildenbrand
2020-09-14 18:33 ` Chris Goldsworthy
2020-09-14 21:52 ` Chris Goldsworthy
2020-09-15 7:53 ` David Hildenbrand
2020-09-17 17:26 ` Chris Goldsworthy
2020-09-17 17:54 ` Chris Goldsworthy
2020-09-24 5:13 ` Chris Goldsworthy
2020-09-28 7:39 ` Christoph Hellwig
[not found] <1599855850-11337-1-git-send-email-cgoldswo@codeaurora.org>
2020-09-11 20:24 ` Chris Goldsworthy
[not found] <1599857630-23714-1-git-send-email-cgoldswo@codeaurora.org>
2020-09-11 20:54 ` Chris Goldsworthy
2020-09-11 21:37 ` Florian Fainelli
2020-09-11 21:42 ` Randy Dunlap
2020-09-14 18:45 ` Chris Goldsworthy
2020-09-14 18:39 ` Chris Goldsworthy
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