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    SubjectRe: [PATCH 01/10] cgroups: Add res_counter_write_u64() API
    On Tue, Oct 04, 2011 at 03:17:51AM +0300, Kirill A. Shutemov wrote:
    > On Mon, Oct 03, 2011 at 09:07:03PM +0200, Frederic Weisbecker wrote:
    > > Extend the resource counter API with a mirror of
    > > res_counter_read_u64() to make it handy to update a resource
    > > counter value from a cgroup subsystem u64 value file.
    > >
    > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    > > Acked-by: Paul Menage <paul@paulmenage.org>
    > > Cc: Li Zefan <lizf@cn.fujitsu.com>
    > > Cc: Johannes Weiner <hannes@cmpxchg.org>
    > > Cc: Aditya Kali <adityakali@google.com>
    > > Cc: Oleg Nesterov <oleg@redhat.com>
    > > Cc: Andrew Morton <akpm@linux-foundation.org>
    > > Cc: Kay Sievers <kay.sievers@vrfy.org>
    > > Cc: Tim Hockin <thockin@hockin.org>
    > > Cc: Tejun Heo <tj@kernel.org>
    > > Cc: Kirill A. Shutemov <kirill@shutemov.name>
    > > Cc: Containers <containers@lists.linux-foundation.org>
    > > ---
    > > include/linux/res_counter.h | 2 ++
    > > kernel/res_counter.c | 25 +++++++++++++++++++------
    > > 2 files changed, 21 insertions(+), 6 deletions(-)
    > >
    > > diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
    > > index c9d625c..1b3fe05 100644
    > > --- a/include/linux/res_counter.h
    > > +++ b/include/linux/res_counter.h
    > > @@ -82,6 +82,8 @@ int res_counter_memparse_write_strategy(const char *buf,
    > > int res_counter_write(struct res_counter *counter, int member,
    > > const char *buffer, write_strategy_fn write_strategy);
    > >
    > > +void res_counter_write_u64(struct res_counter *counter, int member, u64 val);
    > > +
    > > /*
    > > * the field descriptors. one for each member of res_counter
    > > */
    > > diff --git a/kernel/res_counter.c b/kernel/res_counter.c
    > > index 34683ef..0faafcc 100644
    > > --- a/kernel/res_counter.c
    > > +++ b/kernel/res_counter.c
    > > @@ -168,12 +168,26 @@ int res_counter_memparse_write_strategy(const char *buf,
    > > return 0;
    > > }
    > >
    > > +void res_counter_write_u64(struct res_counter *counter, int member, u64 val)
    > > +{
    > > + unsigned long long *target;
    > > + unsigned long flags;
    > > +
    > > + /*
    > > + * We need the lock to protect against concurrent add/dec on 32 bits.
    > > + * No need to ifdef it's seldom used.
    > > + */
    >
    > Should we hace two version of res_counter_write_u64() for 32/64 bit host?
    > As with res_counter_read_u64().

    I thought about it yeah.

    But this is used in rare cases when the user writes the value from the cgroup
    filesystem. In pratice the overhead won't be noticed.
    I fear that would rather uglify the code with more ifdeffery.


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