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    SubjectRe: Fix SWSUSP & !SWAP
    >> > I don't believer I've ever seen things get OOM killed. Instead, page
    >> > cache is discarded until things do fit.
    >> What happens if user allocated pages are filling up all the space,
    >> not page cache? Trust me, it happens ;-)
    > Yep, just because I haven't seen it, doesn't mean a thing. :>. In that
    > case, there are two issues: memory to work in to start with and how to
    > save the image without corrupting it.
    > Regarding #1, there must still be some memory available, mustn't there?
    > swsusp only approx (nrpages in use/256) pages to do its work. Surely
    > we'd always be able to get .4% of the number of pages? Even if we can't
    > get that many, we should be able to adjust the algorithm to be able to
    > suspend a machine with only 10 or so pages available to start with (no,
    > I'm not volunteering to do it! I want to merge with 2.5 and get on to
    > other projects!).

    Well, if you have the pre-reserved area, you just start swapping pages out
    into it. If we need a few pages (like 10) to manage data structures, etc,
    we can just allocate those at boot, and keep them ready.

    > Regarding #2, my algorithm (ie not the version in 2.5 at the mo)
    > separates pages to be saved into 2 types. Pageset1 are pages we expect
    > to be needed during suspend. Pageset2 is those that will definitely not
    > be needed. My algorithm for saving the data goes: Save pageset2 pages to
    > disk then (as per the original/current method) make a copy of pageset1
    > pages (using the pageset2 locations + extra allocated memory if needsbe)
    > and save the copy. Loading the image is the reverse process. Pageset 2
    > currently only consists of all highmem pages + active and inactive list
    > pages.

    Not sure that quite works ... don't you need PTE's to know what to swap
    out? Those can be in highmem. However, all user pages would fit in pageset
    2, I think.

    > If we refined the algorithm, perhaps that would address your
    > issue. The other point here is that since we have to be able to make a
    > copy of pageset1 pages, and since I haven't inlined kmap/unmap in the
    > routine to copy pageset1 pages back on resume (Pavel will say whew to
    > that, I'm sure!), pageset1 has a miximum size of half normal memory. I
    > reckon refining the algoritm so that pageset1 can be [nearly] guaranteed
    > to always be smaller is the better area to focus on, and I'm perfectly
    > happy to try suggestions, particularly when they come in the form of a
    > code fragment that include a call to SetPagePageset2(struct page * page)
    > for the relevant targets :>

    The more I think about this, the more it seems so much simpler to just
    require a reserved swap area the size of your RAM to suspend into. Would
    make the code so much simpler ... forget the option bit I suggested earlier


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