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    SubjectRe: [PATCH] mm: clear __GFP_FS when PF_MEMALLOC_NOIO is set
    On Wed, Sep 03, 2014 at 01:54:54PM +0800, Junxiao Bi wrote:
    > commit 21caf2fc1931 ("mm: teach mm by current context info to not do I/O during memory allocation")
    > introduces PF_MEMALLOC_NOIO flag to avoid doing I/O inside memory allocation, __GFP_IO is cleared
    > when this flag is set, but __GFP_FS implies __GFP_IO, it should also be cleared. Or it may still
    > run into I/O, like in superblock shrinker.
    >
    > Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
    > Cc: joyce.xue <xuejiufei@huawei.com>
    > Cc: Ming Lei <ming.lei@canonical.com>
    > ---
    > include/linux/sched.h | 6 ++++--
    > 1 file changed, 4 insertions(+), 2 deletions(-)
    >
    > diff --git a/include/linux/sched.h b/include/linux/sched.h
    > index 5c2c885..2fb2c47 100644
    > --- a/include/linux/sched.h
    > +++ b/include/linux/sched.h
    > @@ -1936,11 +1936,13 @@ extern void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut,
    > #define tsk_used_math(p) ((p)->flags & PF_USED_MATH)
    > #define used_math() tsk_used_math(current)
    >
    > -/* __GFP_IO isn't allowed if PF_MEMALLOC_NOIO is set in current->flags */
    > +/* __GFP_IO isn't allowed if PF_MEMALLOC_NOIO is set in current->flags
    > + * __GFP_FS is also cleared as it implies __GFP_IO.
    > + */
    > static inline gfp_t memalloc_noio_flags(gfp_t flags)
    > {
    > if (unlikely(current->flags & PF_MEMALLOC_NOIO))
    > - flags &= ~__GFP_IO;
    > + flags &= ~(__GFP_IO | __GFP_FS);
    > return flags;
    > }

    You also need to mask all the shrink_control->gfp_mask
    initialisations in mm/vmscan.c. The current code only masks the page
    reclaim gfp_mask, not those that are passed to the shrinkers.

    Cheers,

    Dave.
    --
    Dave Chinner
    david@fromorbit.com


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