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    SubjectRe: [PATCH v2 0/5] mm: migrate zbud pages
    Hi Krzysztof,

    On 09/11/2013 04:58 PM, Krzysztof Kozlowski wrote:
    > Hi,
    >
    > Currently zbud pages are not movable and they cannot be allocated from CMA
    > (Contiguous Memory Allocator) region. These patches add migration of zbud pages.
    >

    I agree that the migration of zbud pages is important so that system
    will not enter order-0 page fragmentation and can be helpful for page
    compaction/huge pages etc..

    But after I looked at the [patch 4/5], I found it will make zbud very
    complicated.
    I'd prefer to add this migration feature later until current version
    zswap/zbud becomes better enough and more stable.

    Mel mentioned several problems about zswap/zbud in thread "[PATCH v6
    0/5] zram/zsmalloc promotion".

    Like "it's clunky as hell and the layering between zswap and zbud is
    twisty" and "I think I brought up its stalling behaviour during review
    when it was being merged. It would have been preferable if writeback
    could be initiated in batches and then waited on at the very least..
    It's worse that it uses _swap_writepage directly instead of going
    through a writepage ops. It would have been better if zbud pages
    existed on the LRU and written back with an address space ops and
    properly handled asynchonous writeback."

    So I think it would be better if we can address those issues at first
    and it would be easier to address these issues before adding more new
    features. Welcome any ideas.

    --
    Regards,
    -Bob


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