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    SubjectRe: [PATCH 4/4] zsmalloc: zsmalloc: align cache line size
    On 05/11/2012 09:03 AM, Dan Magenheimer wrote:

    >> From: Minchan Kim [mailto:minchan@kernel.org]
    >> Subject: Re: [PATCH 4/4] zsmalloc: zsmalloc: align cache line size
    >>
    >> On 05/08/2012 11:00 PM, Dan Magenheimer wrote:
    >>
    >>>> From: Minchan Kim [mailto:minchan@kernel.org]
    >>>>> zcache can potentially create a lot of pools, so the latter will save
    >>>>> some memory.
    >>>>
    >>>>
    >>>> Dumb question.
    >>>> Why should we create pool per user?
    >>>> What's the problem if there is only one pool in system?
    >>>
    >>> zcache doesn't use zsmalloc for cleancache pages today, but
    >>> that's Seth's plan for the future. Then if there is a
    >>> separate pool for each cleancache pool, when a filesystem
    >>> is umount'ed, it isn't necessary to walk through and delete
    >>> all pages one-by-one, which could take quite awhile.
    >>
    >>>
    >>
    >>> ramster needs one pool for each client (i.e. machine in the
    >>> cluster) for frontswap pages for the same reason, and
    >>> later, for cleancache pages, one per mounted filesystem
    >>> per client
    >>
    >>
    >> Fair enough.
    >> But some subsystems can't want a own pool for not waste unnecessary memory.
    >>
    >> Then, how about this interfaces like slab?
    >>
    >> 1. zs_handle zs_malloc(size_t size, gfp_t flags) - share a pool by many subsystem(like kmalloc)
    >> 2. zs_handle zs_malloc_pool(struct zs_pool *pool, size_t size) - use own pool(like kmem_cache_alloc)
    >>
    >> Any thoughts?
    >
    > I don't have any objections to adding this kind of
    > capability to zsmalloc. But since we are just speculating
    > that this capability would be used by some future
    > kernel subsystem, isn't it normal kernel protocol for
    > this new capability NOT to be added until that future
    > kernel subsystem creates a need for it.


    Now zram makes pool per block device and a embedded system may use zram
    for several block device, ex) swap device, several compressed tmpfs
    In such case, share pool is better than private pool because embedded system
    don't mount/umount frequently on such directories since booting.

    >
    > As I said in reply to the other thread, there is missing
    > functionality in zsmalloc that is making it difficult for
    > it to be used by zcache. It would be good if Seth
    > and Nitin (and any other kernel developers) would work


    So, if you guys post TODO list, it helps fix the direction.

    > on those issues before adding capabilities for non-existent
    > future users of zsmalloc.


    I think it's not urgent than zs_handle mess.

    >
    > Again, that's just my opinion.

    > Dan
    >
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    >



    --
    Kind regards,
    Minchan Kim


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