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    SubjectRe: Fix SWSUSP & !SWAP
    On Thu, 2003-04-24 at 12:45, Martin J. Bligh wrote:
    > > 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!).

    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. 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 :>

    Regards,

    Nigel
    --
    Nigel Cunningham
    495 St Georges Road South, Hastings 4201, New Zealand

    Be diligent to present yourself approved to God as a workman who does
    not need to be ashamed, handling accurately the word of truth.
    -- 2 Timothy 2:14, NASB.

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