Re: [PATCH 2/2] mm: thp: fix transparent_hugepage/defrag = madvise || always

["Zi Yan" <zi.yan@cs.rutgers.edu>]

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<snip>
>
> I do not like overwriting gfp flags like that. It is just ugly and error
> prone. A more proper way would be to handle that at the layer we play
> with __GFP_THISNODE. The resulting diff is larger though.

This makes sense to me.

>
> If there is a general concensus that this is growing too complicated
> then Andrea's patch (the second variant to overwrite gfp mask) is much
> simpler of course but I really detest the subtle gfp rewriting. I still
> believe that all the nasty details should be covered at the single
> place.
>
>
> diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
> index 5228c62af416..bac395f1d00a 100644
> --- a/include/linux/mempolicy.h
> +++ b/include/linux/mempolicy.h
> @@ -139,6 +139,8 @@ struct mempolicy *mpol_shared_policy_lookup(struct shared_policy *sp,
>  struct mempolicy *get_task_policy(struct task_struct *p);
>  struct mempolicy *__get_vma_policy(struct vm_area_struct *vma,
>  		unsigned long addr);
> +struct mempolicy *get_vma_policy(struct vm_area_struct *vma,
> +						unsigned long addr);
>  bool vma_policy_mof(struct vm_area_struct *vma);
>
>  extern void numa_default_policy(void);
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index a703c23f8bab..94472bf9a31b 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -629,21 +629,30 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
>   *	    available
>   * never: never stall for any thp allocation
>   */
> -static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
> +static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma, unsigned long addr)
>  {
>  	const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
> +	gfp_t this_node = 0;
> +	struct mempolicy *pol;
> +
> +#ifdef CONFIG_NUMA
> +	/* __GFP_THISNODE makes sense only if there is no explicit binding */
> +	pol = get_vma_policy(vma, addr);
> +	if (pol->mode != MPOL_BIND)
> +		this_node = __GFP_THISNODE;
> +#endif
>
>  	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
> -		return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY | __GFP_THISNODE);
> +		return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY | this_node);
>  	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
> -		return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM | __GFP_THISNODE;
> +		return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM | this_node;
>  	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags))
>  		return GFP_TRANSHUGE_LIGHT | (vma_madvised ? __GFP_DIRECT_RECLAIM :
> -							     __GFP_KSWAPD_RECLAIM | __GFP_THISNODE);
> +							     __GFP_KSWAPD_RECLAIM | this_node);
>  	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
>  		return GFP_TRANSHUGE_LIGHT | (vma_madvised ? __GFP_DIRECT_RECLAIM :
> -							     __GFP_THISNODE);
> -	return GFP_TRANSHUGE_LIGHT | __GFP_THISNODE;
> +							     this_node);
> +	return GFP_TRANSHUGE_LIGHT | this_node;
>  }
>
>  /* Caller must hold page table lock. */
> @@ -715,7 +724,7 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
>  			pte_free(vma->vm_mm, pgtable);
>  		return ret;
>  	}
> -	gfp = alloc_hugepage_direct_gfpmask(vma);
> +	gfp = alloc_hugepage_direct_gfpmask(vma, haddr);
>  	page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
>  	if (unlikely(!page)) {
>  		count_vm_event(THP_FAULT_FALLBACK);
> @@ -1290,7 +1299,7 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
>  alloc:
>  	if (transparent_hugepage_enabled(vma) &&
>  	    !transparent_hugepage_debug_cow()) {
> -		huge_gfp = alloc_hugepage_direct_gfpmask(vma);
> +		huge_gfp = alloc_hugepage_direct_gfpmask(vma, haddr);
>  		new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
>  	} else
>  		new_page = NULL;
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 9f0800885613..75bbfc3d6233 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1648,7 +1648,7 @@ struct mempolicy *__get_vma_policy(struct vm_area_struct *vma,
>   * freeing by another task.  It is the caller's responsibility to free the
>   * extra reference for shared policies.
>   */
> -static struct mempolicy *get_vma_policy(struct vm_area_struct *vma,
> +struct mempolicy *get_vma_policy(struct vm_area_struct *vma,
>  						unsigned long addr)
>  {
>  	struct mempolicy *pol = __get_vma_policy(vma, addr);

The warning goes away with this change. I am OK with this patch (plus the original one you sent out,
which could be merged with this one).

Thanks.

—
Best Regards,
Yan Zi

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