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    SubjectRe: [PATCH 4/7] mm: defer vmalloc from atomic context
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    On 11/05/2016 06:43 AM, Joel Fernandes wrote:
    > On Mon, Oct 24, 2016 at 8:44 AM, Andrey Ryabinin
    > <aryabinin@virtuozzo.com> wrote:
    >>
    >>
    >> On 10/22/2016 06:17 PM, Christoph Hellwig wrote:
    >>> We want to be able to use a sleeping lock for freeing vmap to keep
    >>> latency down. For this we need to use the deferred vfree mechanisms
    >>> no only from interrupt, but from any atomic context.
    >>>
    >>> Signed-off-by: Christoph Hellwig <hch@lst.de>
    >>> ---
    >>> mm/vmalloc.c | 2 +-
    >>> 1 file changed, 1 insertion(+), 1 deletion(-)
    >>>
    >>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
    >>> index a4e2cec..bcc1a64 100644
    >>> --- a/mm/vmalloc.c
    >>> +++ b/mm/vmalloc.c
    >>> @@ -1509,7 +1509,7 @@ void vfree(const void *addr)
    >>>
    >>> if (!addr)
    >>> return;
    >>> - if (unlikely(in_interrupt())) {
    >>> + if (unlikely(in_atomic())) {
    >>
    >> in_atomic() cannot always detect atomic context, thus it shouldn't be used here.
    >> You can add something like vfree_in_atomic() and use it in atomic call sites.
    >>
    >
    > So because in_atomic doesn't work for !CONFIG_PREEMPT kernels, can we
    > always defer the work in these cases?
    >
    > So for non-preemptible kernels, we always defer:
    >
    > if (!IS_ENABLED(CONFIG_PREEMPT) || in_atomic()) {
    > // defer
    > }
    >
    > Is this fine? Or any other ideas?
    >

    What's wrong with my idea?
    We can add vfree_in_atomic() and use it to free vmapped stacks
    and for any other places where vfree() used 'in_atomict() && !in_interrupt()' context.

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