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    SubjectRe: [f2fs-dev] [PATCH 04/10] f2fs: support IO alignment for DATA and NODE writes
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    On 2017/1/5 7:44, Jaegeuk Kim wrote:
    > On 01/04, Chao Yu wrote:
    >> Hi Jaegeuk,
    >>
    >> On 2016/12/31 2:51, Jaegeuk Kim wrote:
    >>> This patch implements IO alignment by filling dummy blocks in DATA and NODE
    >>> write bios. If we can guarantee, for example, 32KB or 64KB for such the IOs,
    >>> we can eliminate underlying dummy page problem which FTL conducts in order to
    >>> close MLC or TLC partial written pages.
    >>>
    >>> Note that,
    >>> - it requires "-o mode=lfs".
    >>> - IO size should be power of 2, not exceed BIO_MAX_PAGES, 256.
    >>> - read IO is still 4KB.
    >>> - do checkpoint at fsync, if dummy NODE page was written.
    >>
    >> Which scenario we can benefit from? Any numbers?
    >
    > I described it in the patch. This is not targetting for performance improvement
    > for now, but to address the dummy page write problem in FTL so that we can later
    > implement very simple host-level FTL on top of open-channel SSD.

    Alright, if we are doing this since FTL implementation is moved up, so I can
    understand that.

    Thanks,

    >
    >> I doubt that there are some potential side-effect points:
    >> - write amplification will be more serious than before
    >> - free space will be more fragmented since dummy blocks is separated in whole
    >> address space
    >> - there is less chance to merge small(unaligned) IOs in block layer
    >
    > I agree, so I just added this as a mount option experimentally.
    > One point would be that, if f2fs doesn't do this, FTL should do it. So I think,
    > from the system point of view, f2fs is a better layer to do it.
    >
    > Thanks,
    >
    >>
    >> Thoughts?
    >>
    >> Thanks,
    >
    > .
    >

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