[lkml]   [2006]   [Jul]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRFC: Block size > PAGE_SIZE
    I have idea to lift software based limitation of 4K
    maximum block size of block devices.

    There are some devices that have bigger that 4K block
    size. The most notable are packet driven CD/DVD
    recorders, but for example Flash chips cannot erase
    blocks that are bigger that 64K of even more.

    The main reason for this limitation is the fact that
    both buffer and page cache are stored in pages, and
    each page have set of buffers that is pointed by it's
    private field. So a page must contain at least one
    buffer and thus buffer cannot be larger that 4K , the
    IA32 default page size.

    The extent based filesystems can also benefit from
    bigger block size , they will be able to read a
    cluster at time

    My idea is storing a sector in number of pages.

    Each buffer_head will have addition filed ->next that
    will point in circuit to next buffer_head that stores
    data from the same sector
    actually it is possible not to use this ->next field
    because buffer_heads are linked in list of same page
    buffer_heads. but im my case page will contain only
    one buffer head so I can reuse this field.

    From FS point of view , it may look difficult to
    implement big block sizes because filesystems are not
    aware of ether linked list of buffer_heads nor of big
    block sizes.

    But this can be fixed very easy. set_blocksize will
    have addition flags parameter and all filesystems that
    are unaware of new design or don't need big block
    sized will pass 0 as this parameter. and they won't be
    allowed to use new design. New or modified filesystems
    will pass a flag and bigger that 4K block size to this
    function, and then after each __getblk they will
    examine not only returned buffer_head but also the
    linked ones.

    default address space operations will be changed too
    to support both small and big block sizes.

    I thought a lot about changes is those functions but
    it seems that changes small enough.

    I didn't yet implemented this idea , because I want to
    know whenever you like this idea or not. After all
    this is not a simply work.

    Do You Yahoo!?
    Tired of spam? Yahoo! Mail has the best spam protection around
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2006-07-20 12:53    [W:0.020 / U:8.616 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site