linux-kernel - Re: swap_cluster

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Message-ID: <87o9y17daf.fsf@yhuang-dev.intel.com>
Date:   Fri, 17 Feb 2017 10:37:44 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     "Huang\, Ying" <ying.huang@...el.com>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: swap_cluster_info lockdep splat

"Huang, Ying" <ying.huang@...el.com> writes:

> Hi, Hugh,
>
> Hugh Dickins <hughd@...gle.com> writes:
>
>> On Thu, 16 Feb 2017, Tim Chen wrote:
>>> 
>>> > I do not understand your zest for putting wrappers around every little
>>> > thing, making it all harder to follow than it need be.  Here's the patch
>>> > I've been running with (but you have a leak somewhere, and I don't have
>>> > time to search out and fix it: please try sustained swapping and swapoff).
>>> > 
>>> 
>>> Hugh, trying to duplicate your test case.  So you were doing swapping,
>>> then swap off, swap on the swap device and restart swapping?
>>
>> Repeated pair of make -j20 kernel builds in 700M RAM, 1.5G swap on SSD,
>> 8 cpus; one of the builds in tmpfs, other in ext4 on loop on tmpfs file;
>> sizes tuned for plenty of swapping but no OOMing (it's an ancient 2.6.24
>> kernel I build, modern one needing a lot more space with a lot less in use).
>>
>> How much of that is relevant I don't know: hopefully none of it, it's
>> hard to get the tunings right from scratch.  To answer your specific
>> question: yes, I'm not doing concurrent swapoffs in this test showing
>> the leak, just waiting for each of the pair of builds to complete,
>> then tearing down the trees, doing swapoff followed by swapon, and
>> starting a new pair of builds.
>>
>> Sometimes it's the swapoff that fails with ENOMEM, more often it's a
>> fork during build that fails with ENOMEM: after 6 or 7 hours of load
>> (but timings show it getting slower leading up to that).  /proc/meminfo
>> did not give me an immediate clue, Slab didn't look surprising but
>> I may not have studied close enough.
>
> Thanks for you information!
>
> Memory newly allocated in the mm-swap series are allocated via vmalloc,
> could you find anything special for vmalloc in /proc/meminfo?

I found a potential issue in the mm-swap series, could you try the
patches as below?

Best Regards,
Huang, Ying

----------------------------------------------------->
>From 943494339bd5bc321b8f36f286bc143ac437719b Mon Sep 17 00:00:00 2001
From: Huang Ying <ying.huang@...el.com>
Date: Fri, 17 Feb 2017 10:31:37 +0800
Subject: [PATCH] Debug memory leak

---
 mm/swap_state.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 2126e9ba23b2..473b71e052a8 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -333,7 +333,7 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 		 * else swap_off will be aborted if we return NULL.
 		 */
 		if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
-			return NULL;
+			break;
 
 		/*
 		 * Get a new page to read into from swap.
-- 
2.11.0