[lkml]   [2007]   [Apr]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: Pagecache: find_or_create_page does not call a proper page allocator function
    On Tue, 24 Apr 2007, Christoph Lameter wrote:
    > On Tue, 24 Apr 2007, Hugh Dickins wrote:
    > > I've not yet looked at the patch under discussion, but this remark
    > > prompts me... a couple of days ago I got very worried by the various
    > > hard-wired GFP_HIGHUSER allocations in mm/migrate.c and mm/mempolicy.c,
    > > and wondered how those would work out if someone has a blockdev mmap'ed.
    > I hope you are not confused by the fact that memory policies are only
    > ever applied to one zone on a node. This is either HIGHMEM or NORMAL.
    > There is no memory policy support for other than the highest zone.

    I was certainly ignorant of that; but I'm not convinced it eliminates
    the potential issue. For a start, sys_move_pages seems not to involve
    mempolicies at all - I don't see what prevents it migrating blockdev
    pages away from the only node which has NORMAL memory.

    > Metadata is not movable nor subject to memory policies.
    > It will never be mapped into a process space.

    Not as metadata, no. But someone (let's hope only root, though I may
    be wrong on that) can map any part of the block device into userspace.

    > > yup. wherever we dereference buffer_head.b_data we're touching
    > > page_address(buffer_head.b_page) without kmapping.
    > Yes but before we get there we will bounce pagecache pages into an area
    > where we do not need kmap.

    Again, I'm not convinced: bouncing gets done for the I/O,
    but where is it done to meet the filesystem's expectations?

    On the other hand, as I said, I've seen no problem myself in practice.
    However, if there is no problem, why do block devices demand GFP_USER?

    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: 2007-04-24 20:57    [W:0.023 / U:11.524 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site