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SubjectRe: [PATCH v8 1/4] mm/cma: Add PF flag to force non cma alloc
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On 2/27/19 3:47 PM, Aneesh Kumar K.V wrote:
> This patch adds PF_MEMALLOC_NOCMA which make sure any allocation in that context
> is marked non-movable and hence cannot be satisfied by CMA region.
>
> This is useful with get_user_pages_longterm where we want to take a page pin by
> migrating pages from CMA region. Marking the section PF_MEMALLOC_NOCMA ensures
> that we avoid unnecessary page migration later.
>
> Suggested-by: Andrea Arcangeli <aarcange@redhat.com>
> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

+CC scheduler guys

Do we really take the last available PF flag just so that "we avoid
unnecessary page migration later"?
If yes, that's a third PF_MEMALLOC flag, should we get separate variable
for gfp context at this point?
Also I don't like the name PF_MEMALLOC_NOCMA, as it's unnecessarily tied
to CMA. If anything it should be e.g. PF_MEMALLOC_NOMOVABLE.

Thanks.

> ---
> include/linux/sched.h | 1 +
> include/linux/sched/mm.h | 48 +++++++++++++++++++++++++++++++++-------
> 2 files changed, 41 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index f9b43c989577..dfa90088ba08 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1403,6 +1403,7 @@ extern struct pid *cad_pid;
> #define PF_UMH 0x02000000 /* I'm an Usermodehelper process */
> #define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_allowed */
> #define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */
> +#define PF_MEMALLOC_NOCMA 0x10000000 /* All allocation request will have _GFP_MOVABLE cleared */
> #define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */
> #define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezable */
> #define PF_SUSPEND_TASK 0x80000000 /* This thread called freeze_processes() and should not be frozen */
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 3bfa6a0cbba4..0cd9f10423fb 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -148,17 +148,25 @@ static inline bool in_vfork(struct task_struct *tsk)
> * Applies per-task gfp context to the given allocation flags.
> * PF_MEMALLOC_NOIO implies GFP_NOIO
> * PF_MEMALLOC_NOFS implies GFP_NOFS
> + * PF_MEMALLOC_NOCMA implies no allocation from CMA region.
> */
> static inline gfp_t current_gfp_context(gfp_t flags)
> {
> - /*
> - * NOIO implies both NOIO and NOFS and it is a weaker context
> - * so always make sure it makes precedence
> - */
> - if (unlikely(current->flags & PF_MEMALLOC_NOIO))
> - flags &= ~(__GFP_IO | __GFP_FS);
> - else if (unlikely(current->flags & PF_MEMALLOC_NOFS))
> - flags &= ~__GFP_FS;
> + if (unlikely(current->flags &
> + (PF_MEMALLOC_NOIO | PF_MEMALLOC_NOFS | PF_MEMALLOC_NOCMA))) {
> + /*
> + * NOIO implies both NOIO and NOFS and it is a weaker context
> + * so always make sure it makes precedence
> + */
> + if (current->flags & PF_MEMALLOC_NOIO)
> + flags &= ~(__GFP_IO | __GFP_FS);
> + else if (current->flags & PF_MEMALLOC_NOFS)
> + flags &= ~__GFP_FS;
> +#ifdef CONFIG_CMA
> + if (current->flags & PF_MEMALLOC_NOCMA)
> + flags &= ~__GFP_MOVABLE;
> +#endif
> + }
> return flags;
> }
>
> @@ -248,6 +256,30 @@ static inline void memalloc_noreclaim_restore(unsigned int flags)
> current->flags = (current->flags & ~PF_MEMALLOC) | flags;
> }
>
> +#ifdef CONFIG_CMA
> +static inline unsigned int memalloc_nocma_save(void)
> +{
> + unsigned int flags = current->flags & PF_MEMALLOC_NOCMA;
> +
> + current->flags |= PF_MEMALLOC_NOCMA;
> + return flags;
> +}
> +
> +static inline void memalloc_nocma_restore(unsigned int flags)
> +{
> + current->flags = (current->flags & ~PF_MEMALLOC_NOCMA) | flags;
> +}
> +#else
> +static inline unsigned int memalloc_nocma_save(void)
> +{
> + return 0;
> +}
> +
> +static inline void memalloc_nocma_restore(unsigned int flags)
> +{
> +}
> +#endif
> +
> #ifdef CONFIG_MEMCG
> /**
> * memalloc_use_memcg - Starts the remote memcg charging scope.
>

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