linux-kernel - [PATCH 0/4] zswap bugfix: memory leaks and other problem

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Date:	Fri, 23 Aug 2013 18:12:33 +0800
From:	Weijie Yang <weijie.yang@...sung.com>
To:	minchan@...nel.org, bob.liu@...cle.com, sjenning@...ux.vnet.ibm.com
Cc:	weijie.yang.kh@...il.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 0/4] zswap bugfix: memory leaks and other problem

This patch series fix a few bugs in zswap based on Linux-3.11-rc6.

Corresponding mail thread see: lkml.org/lkml/2013/8/18/59 .

These issues fixed are:
1. memory leaks when re-swapon
2. potential problem which store and reclaim functions is called recursively 
3. memory leaks when invalidate and reclaim occur simultaneously 
4. unnecessary page scanning

Issues discussed in that mail thread NOT fixed as it happens rarely or not a big problem:
1. a "theoretical race condition" when reclaim page 
when a handle alloced from zbud, zbud considers this handle is used validly by upper(zswap) and can be a candidate for reclaim.
But zswap has to initialize it such as setting swapentry and adding it to rbtree. so there is a race condition, such as:
thread 0: obtain handle x from zbud_alloc 
thread 1: zbud_reclaim_page is called 
thread 1: callback zswap_writeback_entry to reclaim handle x 
thread 1: get swpentry from handle x (it is random value now) 
thread 1: bad thing may happen 
thread 0: initialize handle x with swapentry

2. frontswap_map bitmap not cleared after zswap reclaim 
Frontswap uses frontswap_map bitmap to track page in "backend" implementation, 
when zswap reclaim a page, the corresponding bitmap record is not cleared.

mm/zswap.c |   35 ++++++++++++++++++++++++-----------
 1 files changed, 24 insertions(+), 11 deletions(-)

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