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    SubjectRe: [PATCH] regression: vmalloc easily fail.
    Glauber Costa wrote:
    > Commit db64fe02258f1507e13fe5212a989922323685ce broke
    > KVM (the symptom) for me. The cause is that vmalloc
    > allocations fail, despite of the fact that /proc/meminfo
    > shows plenty of vmalloc space available.
    >
    > After some investigation, it seems to me that the current
    > way to compute the next addr in the rb-tree transversal
    > leaves a spare page between each allocation. After a few
    > allocations, regardless of their size, we run out of vmalloc
    > space.
    >
    >
    > while (addr + size >= first->va_start && addr + size <= vend) {
    > - addr = ALIGN(first->va_end + PAGE_SIZE, align);
    > + addr = ALIGN(first->va_end, align);
    >
    > n = rb_next(&first->rb_node);
    > if (n)
    >

    I'm guessing that the missing comment explains that this is intentional,
    to trap buffer overflows?

    (okay that was a cheap shot. I don't comment nearly enough either)

    Even if you leave a page between allocations, I don't see how you can
    fail a one page allocation, unless you've allocated at least N/2 pages
    (where N is the size of the vmalloc space in pages).

    --
    I have a truly marvellous patch that fixes the bug which this
    signature is too narrow to contain.



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