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    SubjectRe: upcoming kerneloops.org item: get_page_from_freelist
    On Thu, Jun 25, 2009 at 01:18:59PM -0700, David Rientjes wrote:
    > Isn't there also a problem in jbd2_journal_write_metadata_buffer(),
    > though?
    >
    > tmp = jbd2_alloc(bh_in->b_size, GFP_NOFS);
    ...
    > memcpy(tmp, mapped_data + new_offset, jh2bh(jh_in)->b_size);
    >
    > jbd2_alloc() is just a wrapper to __get_free_pages() and if it fails, it
    > appears as though the memcpy() would cause a NULL pointer.

    Nicely spotted. Yeah, that's a bug; we need to do something about
    that one, too. And what we're doing is a bit silly; it may make sense
    to use __get_free_pages if filesystem blocksize == PAGE_SIZE, but
    otherwise we should be using a sub-page allocator. Right now, we're
    chewing up a 16k PPC page for every 4k filesystem metadata page
    allocated in journal_write_metadata_buffer(), and on x86, for the
    (admittedly uncommon) 1k block filesystem, we'd be chewing up a 4k
    page for a 1k block buffer.


    Both of these problems exist for both ext3 and ext4.

    - Ted


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