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    SubjectRe: [PATCH 00/23] per device dirty throttling -v8
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    On Sat, 2007-08-04 at 17:48 -0400, Theodore Tso wrote:
    > On Sat, Aug 04, 2007 at 01:13:19PM -0700, Arjan van de Ven wrote:
    > > there is another trick possible (more involved though, Al will have to
    > > jump in on that one I suspect): Have 2 types of "dirty inode" states;
    > > one is the current dirty state (meaning the full range of ext3
    > > transactions etc) and "lighter" state of "atime-dirty"; which will not
    > > do the background syncs or journal transactions (so if your machine
    > > crashes, you lose the atime update) but it does keep atime for most
    > > normal cases and keeps it standard compliant "except after a crash".
    >
    > That would make us standards compliant (POSIX explicitly says that
    > what happens after a unclean shutdown is Unspecified) and it would
    > make things a heck of a lot faster. However, there is a potential
    > problem which is that it will keep a large number of inodes pinned in
    > memory, which is its own problem. So there would have to be some way
    > to force the atime updates to be merged when under memory pressure,
    > and and perhaps on some much longer background interval (i.e., every
    > hour or so).

    on the journalling side this would be one transaction (not 5 milion)
    and... since inodes are grouped on disk, you can even get some better
    coalescing this way...

    Wonder if we could do inode-grouping smartly; eg if we HAVE to write
    inode X, also write out the atime-dirty inodes in range X-Y to X+Y
    (where Y is some tunable) in the same IO..


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