linux-kernel - [PATCH v2 0/4] mm/zswap bugfix: memory leaks and other problems

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Date:	Fri, 06 Sep 2013 13:15:08 +0800
From:	Weijie Yang <weijie.yang@...sung.com>
To:	sjenning@...ux.vnet.ibm.com
Cc:	minchan@...nel.org, bob.liu@...cle.com, weijie.yang.kh@...il.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/4] mm/zswap bugfix: memory leaks and other problems

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

v1 --> v2
	- free memory in zswap_frontswap_invalidate_area (in patch 1)
	- fix whitespace corruption (line wrapping)

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

These issues fixed/optimized are:

 1. memory leaks when re-swapon
 
 2. memory leaks when invalidate and reclaim occur concurrently
 
 3. avoid unnecessary page scanning
 
 4. use GFP_NOIO instead of GFP_KERNEL to avoid zswap store and reclaim 
functions called recursively

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 |   34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

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