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    SubjectRe: [PATCH v1] mm/vmalloc: fix exact allocations with an alignment > 1
    >
    > So the idea is that once we run into a dead end because we took a left
    > subtree, we rollback to the next possible rigth subtree and try again.
    > If we run into another dead end, we repeat ... thus, this can now happen
    > more than once.
    >
    > I assume the only implication is that this can now be slower in some
    > corner cases with larger alignment, because it might take longer to find
    > something suitable. Fair enough.
    >
    Yep, your understanding is correct regarding the tree traversal. If no
    suitable block
    is found in left sub-tree we roll-back and check right one. So it can
    be(the scanning)
    more than one time.

    I did some performance analyzing using vmalloc test suite to figure
    out a performance
    loss for allocations with specific alignment. On that syntactic test i
    see approx. 30%
    of degradation:

    2.225 microseconds vs 1.496 microseconds. That time includes both
    vmalloc() and vfree()
    calls. I do not consider it as a big degrade, but from the other hand
    we can still adjust the
    search length for alignments > one page:

    # add it on top of previous proposal and search length instead of size
    length = align > PAGE_SIZE ? size + align:size;

    in that case we solve a KASAN issue + do not introduce a degrade. For
    the PAGE_SIZE
    alignment all free blocks are aligned to it anyway. As for users which
    uses a fixed range
    that is same as a requested size and at the same time want to apply a
    special alignment
    is not considered as a common case, also we do not have such users.

    Thoughts?

    > >
    > > Could you please help and test the KASAN use case?
    >
    > Just tried it, works just fine with KASAN and makes sense in general,
    > thanks!
    >
    Good!

    Sorry for the delay.

    --
    Uladzislau Rezki

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