On 09/04/2014 05:23 PM, Dave Chinner wrote:
> 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@xxxxxxxxxx>
>> Cc: joyce.xue <xuejiufei@xxxxxxxxxx>
>> Cc: Ming Lei <ming.lei@xxxxxxxxxxxxx>
>> ---
>> 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.
Yes, there are some shrink_control->gfp_mask not masked in vmscan.c in
the following functions. Beside this, all seemed be masked from direct
reclaim path by memalloc_noio_flags().
-reclaim_clean_pages_from_list()
used by alloc_contig_range(), this function is invoked in hugetlb and
cma, for hugetlb, it should be safe as only userspace use it. I am not
sure about the cma.
David & Andrew, may you share your idea about whether cma is affected?
-mem_cgroup_shrink_node_zone()
-try_to_free_mem_cgroup_pages()
These two are used by mem cgroup, as no kernel thread can be assigned
into such cgroup, so i think, no need mask.
-balance_pgdat()
used by kswapd, no need mask.
-shrink_all_memory()
used by hibernate, should be safe with GFP_FS/IO.
Thanks,
Junxiao.
>
> Cheers,
>
> Dave.
>
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