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SubjectRe: [PATCH 0/3] ramzswap: Eliminate stale data in compressed memory
On 03/05/2010 03:52 PM, Nitin Gupta wrote:
> ramzswap driver creates RAM based block devices which can be
> used (only) as swap disks. Pages swapped to these disks are
> compressed and stored in memory itself.
>
> However, these devices do not get any notification when a swap
> slot is freed (swap_map[i] reaches 0). So, we cannot free memory
> allocated corresponding to this swap slot. Such stale data can
> quickly accumulate in (compressed) memory defeating the whole
> purpose of such devices.
>
> To overcome this problem, we now add a callback in 'struct swap_info_struct'
> which is called as soon as a swap slot is freed.
>
> Adding handler for this callback:
> swapon notifier --> set_swap_free_notify(swap_type, fn)
>
> Removing handler:
> swapoff notifier --> set_swap_free_notify(swap_type, NULL)
>
>
> Alternative approaches:
> 1) Add callback directly in 'struct block_device_operations' but
> that is considered too hacky.
> 2) Use swap discard mechanism: It involves unncessary overhead of
> allocating 'discard bio' requests and its too slow to serve ramzswap
> needs.
>
> drivers/staging/ramzswap/ramzswap_drv.c | 91 +++++++++++++++++++++++++++++
> drivers/staging/ramzswap/ramzswap_drv.h | 1 +
> drivers/staging/ramzswap/ramzswap_ioctl.h | 1 +
> include/linux/swap.h | 16 +++++-
> mm/swapfile.c | 78 ++++++++++++++++++++++++
> 5 files changed, 185 insertions(+), 2 deletions(-)
>


Any chance it can go into 2.6.34? Any comments?


Thanks,
Nitin


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