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    SubjectRe: [PATCH] swsusp: separate swap-writing/reading code
    Date
    On Friday 24 March 2006 00:58, Andrew Morton wrote:
    > "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
    > >
    > > > I guess I missed this one somehow. Using a bitmap for allocated swap is really
    > > > inefficient because the values are usually not fragmented much. Extents would
    > > > have been a far better choice.
    > >
    > > I agree it probably may be improved. Still it seems to be good enough. Further,
    > > it's more efficient than the previous solution, so I consider it as an improvement.
    > > Also this code has been tested for quite some time in -mm and appears to
    > > behave properly, at least we haven't got any bug reports related to it so far.
    >
    > I think that temporarily allocating 1/32768th of total memory here is
    > reasonable, especially as it's not all allocated in a contiguous hunk.
    >
    > > Currently I'm not working on any better solution. If you can provide any
    > > patches to implement one, please submit them, but I think they'll have to be
    > > tested for as long as this code, in -mm.
    >
    > I was a little saddened by the open-coded approach. I'd expect that both
    > radix-trees and idr-trees could be used in this application. Probably the
    > former. (Radix-trees should have been designed from day one to store
    > `unsigned long's, not void*'s, so unless we change that, this application
    > will need to use typecasts when converting between void*'s and the stored
    > BITS_PER_LONG bitmaps).

    Perhaps we can use radix-trees here. Frankly, I haven't investigated this
    possibility yet, because this part is not very high on my priority list for
    improvements. :-)

    First, I'd like to get the userland suspend out so people can benefit from the
    userland interface. Second, I think we can save much more memory if we
    use bitmaps for the image metadata, but that will require a lot of work.
    Then, there's the problem of the system responsiveness after resume,
    and the "USB storage not available after resume" problem that I wouldn't
    like to drop on the floor. Not to mention device driver problems.

    Greetings,
    Rafael
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