Prev: [PATCH] x86/kvm: Show guest system/user cputime in cpustat
Next: fs: fat: use hex_asc_lo/hex_asc_hi instead of custom one
From: Hugh Dickins on 11 Mar 2010 02:30
On Fri, 5 Mar 2010, 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(-)

This is one of the various solutions I disliked already, isn't it?

To me this is just a more convoluted and obscure variant of the
block_device_operations swap_slot_free_notify patch you had in mmotm,
which Linus has rejected.

I admit, I did not understand at all what Linus was proposing with
readpage, writepage and address_space_operations: I kept quiet in
the hope that you'd understand where I didn't!

Hugh
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
 | 
Pages: 1
Prev: [PATCH] x86/kvm: Show guest system/user cputime in cpustat
Next: fs: fat: use hex_asc_lo/hex_asc_hi instead of custom one