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    SubjectRe: [PATCH 2/2] blktrace: limit allowed total trace buffer size
    On Tue, Mar 30, 2021 at 10:57:04AM +0800, Su Yue wrote:
    >
    > On Tue 23 Mar 2021 at 16:14, Ming Lei <ming.lei@redhat.com> wrote:
    >
    > > On some ARCHs, such as aarch64, page size may be 64K, meantime there may
    > > be lots of CPU cores. relay_open() needs to allocate pages on each CPU
    > > blktrace, so easily too many pages are taken by blktrace. For example,
    > > on one ARM64 server: 224 CPU cores, 16G RAM, blktrace finally got
    > > allocated 7GB in case of 'blktrace -b 8192' which is used by
    > > device-mapper
    > > test suite[1]. This way could cause OOM easily.
    > >
    > > Fix the issue by limiting max allowed pages to be 1/8 of
    > > totalram_pages().
    > >
    > > [1] https://github.com/jthornber/device-mapper-test-suite.git
    > >
    > > Signed-off-by: Ming Lei <ming.lei@redhat.com>
    > > ---
    > > kernel/trace/blktrace.c | 32 ++++++++++++++++++++++++++++++++
    > > 1 file changed, 32 insertions(+)
    > >
    > > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
    > > index c221e4c3f625..8403ff19d533 100644
    > > --- a/kernel/trace/blktrace.c
    > > +++ b/kernel/trace/blktrace.c
    > > @@ -466,6 +466,35 @@ static void blk_trace_setup_lba(struct blk_trace
    > > *bt,
    > > }
    > > }
    > >
    > > +/* limit total allocated buffer size is <= 1/8 of total pages */
    > > +static void validate_and_adjust_buf(struct blk_user_trace_setup *buts)
    > > +{
    > > + unsigned buf_size = buts->buf_size;
    > > + unsigned buf_nr = buts->buf_nr;
    > > + unsigned long max_allowed_pages = totalram_pages() >> 3;
    > > + unsigned long req_pages = PAGE_ALIGN(buf_size * buf_nr) >> PAGE_SHIFT;
    > > +
    > > + if (req_pages * num_online_cpus() <= max_allowed_pages)
    > > + return;
    > > +
    > > + req_pages = DIV_ROUND_UP(max_allowed_pages, num_online_cpus());
    > > +
    > > + if (req_pages == 0) {
    > > + buf_size = PAGE_SIZE;
    > > + buf_nr = 1;
    > > + } else {
    > > + buf_size = req_pages << PAGE_SHIFT / buf_nr;
    > >
    > Should it be:
    > buf_size = (req_pages << PAGE_SHIFT) / buf_nr;
    > ?
    > The priority of '<<' is lower than '/', right? :)

    Good catch, thanks!

    --
    Ming

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