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SubjectRe: [PATCH v3 0/3] mm/zswap bugfix: memory leaks and other problems
On Mon, Sep 23, 2013 at 04:19:36PM +0800, Weijie Yang wrote:
> This patch series fix a few bugs in mm/zswap based on Linux-3.11.
>
> v2 --> v3
> - keep GFP_KERNEL flag

Why do you drop this?

It's plain BUG. I read Bob's reply but it couldn't justify to let the pain
remain. First of all, let's fix it and better idea could come later.

>
> 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
>
>
> Issues discussed in that mail thread NOT fixed as it happens rarely or
> not a big problem or controversial:
>
> 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.
>
> 3. the potential that zswap store and reclaim functions called recursively
>
>
> mm/zswap.c | 28 ++++++++++++++++++++--------
> 1 file changed, 20 insertions(+), 8 deletions(-)
>
> --
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--
Kind regards,
Minchan Kim


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