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SubjectRe: [patch for-4.20] Revert "mm, thp: consolidate THP gfp handling into alloc_hugepage_direct_gfpmask"
On Thu 06-12-18 14:00:20, David Rientjes wrote:
> This reverts commit 89c83fb539f95491be80cdd5158e6f0ce329e317.
>
> There are a couple of issues with 89c83fb539f9 independent of its partial
> revert in 2f0799a0ffc0 ("mm, thp: restore node-local hugepage
> allocations"):
>
> Firstly, the interaction between alloc_hugepage_direct_gfpmask() and
> alloc_pages_vma() is racy wrt __GFP_THISNODE and MPOL_BIND.
> alloc_hugepage_direct_gfpmask() makes sure not to set __GFP_THISNODE for
> an MPOL_BIND policy but the policy used in alloc_pages_vma() may not be
> the same for shared vma policies, triggering the WARN_ON_ONCE() in
> policy_node().

Could you share a test case?

> Secondly, prior to 89c83fb539f9, alloc_pages_vma() implemented a somewhat
> different policy for hugepage allocations, which were allocated through
> alloc_hugepage_vma(). For hugepage allocations, if the allocating
> process's node is in the set of allowed nodes, allocate with
> __GFP_THISNODE for that node (for MPOL_PREFERRED, use that node with
> __GFP_THISNODE instead).

Why is it wrong to fallback to an explicitly configured mbind mask?

> This was changed for shmem_alloc_hugepage() to
> allow fallback to other nodes in 89c83fb539f9 as it did for new_page() in
> mm/mempolicy.c which is functionally different behavior and removes the
> requirement to only allocate hugepages locally.

Also why should new_page behave any differently for THP from any other
pages? There is no fallback allocation for those and so the mbind could
easily fail. So what is the actual rationale?

> The latter should have been reverted as part of 2f0799a0ffc0 as well.
>
> Fully revert 89c83fb539f9 so that hugepage allocation policy is fully
> restored and there is no race between alloc_hugepage_direct_gfpmask() and
> alloc_pages_vma().
>
> Fixes: 89c83fb539f9 ("mm, thp: consolidate THP gfp handling into alloc_hugepage_direct_gfpmask")
> Fixes: 2f0799a0ffc0 ("mm, thp: restore node-local hugepage allocations")
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
> include/linux/gfp.h | 12 ++++++++----
> mm/huge_memory.c | 27 +++++++++++++--------------
> mm/mempolicy.c | 32 +++++++++++++++++++++++++++++---
> mm/shmem.c | 2 +-
> 4 files changed, 51 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -510,18 +510,22 @@ alloc_pages(gfp_t gfp_mask, unsigned int order)
> }
> extern struct page *alloc_pages_vma(gfp_t gfp_mask, int order,
> struct vm_area_struct *vma, unsigned long addr,
> - int node);
> + int node, bool hugepage);
> +#define alloc_hugepage_vma(gfp_mask, vma, addr, order) \
> + alloc_pages_vma(gfp_mask, order, vma, addr, numa_node_id(), true)
> #else
> #define alloc_pages(gfp_mask, order) \
> alloc_pages_node(numa_node_id(), gfp_mask, order)
> -#define alloc_pages_vma(gfp_mask, order, vma, addr, node)\
> +#define alloc_pages_vma(gfp_mask, order, vma, addr, node, false)\
> + alloc_pages(gfp_mask, order)
> +#define alloc_hugepage_vma(gfp_mask, vma, addr, order) \
> alloc_pages(gfp_mask, order)
> #endif
> #define alloc_page(gfp_mask) alloc_pages(gfp_mask, 0)
> #define alloc_page_vma(gfp_mask, vma, addr) \
> - alloc_pages_vma(gfp_mask, 0, vma, addr, numa_node_id())
> + alloc_pages_vma(gfp_mask, 0, vma, addr, numa_node_id(), false)
> #define alloc_page_vma_node(gfp_mask, vma, addr, node) \
> - alloc_pages_vma(gfp_mask, 0, vma, addr, node)
> + alloc_pages_vma(gfp_mask, 0, vma, addr, node, false)
>
> extern unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order);
> extern unsigned long get_zeroed_page(gfp_t gfp_mask);
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -629,30 +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, unsigned long addr)
> +static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
> {
> const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
> - const gfp_t gfp_mask = GFP_TRANSHUGE_LIGHT | __GFP_THISNODE;
>
> /* Always do synchronous compaction */
> if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
> - return GFP_TRANSHUGE | __GFP_THISNODE |
> - (vma_madvised ? 0 : __GFP_NORETRY);
> + return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY);
>
> /* Kick kcompactd and fail quickly */
> if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
> - return gfp_mask | __GFP_KSWAPD_RECLAIM;
> + return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM;
>
> /* Synchronous compaction if madvised, otherwise kick kcompactd */
> if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags))
> - return gfp_mask | (vma_madvised ? __GFP_DIRECT_RECLAIM :
> - __GFP_KSWAPD_RECLAIM);
> + return GFP_TRANSHUGE_LIGHT |
> + (vma_madvised ? __GFP_DIRECT_RECLAIM :
> + __GFP_KSWAPD_RECLAIM);
>
> /* Only do synchronous compaction if madvised */
> if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
> - return gfp_mask | (vma_madvised ? __GFP_DIRECT_RECLAIM : 0);
> + return GFP_TRANSHUGE_LIGHT |
> + (vma_madvised ? __GFP_DIRECT_RECLAIM : 0);
>
> - return gfp_mask;
> + return GFP_TRANSHUGE_LIGHT;
> }
>
> /* Caller must hold page table lock. */
> @@ -724,8 +724,8 @@ 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, haddr);
> - page = alloc_pages_vma(gfp, HPAGE_PMD_ORDER, vma, haddr, numa_node_id());
> + gfp = alloc_hugepage_direct_gfpmask(vma);
> + page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
> if (unlikely(!page)) {
> count_vm_event(THP_FAULT_FALLBACK);
> return VM_FAULT_FALLBACK;
> @@ -1295,9 +1295,8 @@ 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, haddr);
> - new_page = alloc_pages_vma(huge_gfp, HPAGE_PMD_ORDER, vma,
> - haddr, numa_node_id());
> + huge_gfp = alloc_hugepage_direct_gfpmask(vma);
> + 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
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1116,8 +1116,8 @@ static struct page *new_page(struct page *page, unsigned long start)
> } else if (PageTransHuge(page)) {
> struct page *thp;
>
> - thp = alloc_pages_vma(GFP_TRANSHUGE, HPAGE_PMD_ORDER, vma,
> - address, numa_node_id());
> + thp = alloc_hugepage_vma(GFP_TRANSHUGE, vma, address,
> + HPAGE_PMD_ORDER);
> if (!thp)
> return NULL;
> prep_transhuge_page(thp);
> @@ -2011,6 +2011,7 @@ static struct page *alloc_page_interleave(gfp_t gfp, unsigned order,
> * @vma: Pointer to VMA or NULL if not available.
> * @addr: Virtual Address of the allocation. Must be inside the VMA.
> * @node: Which node to prefer for allocation (modulo policy).
> + * @hugepage: for hugepages try only the preferred node if possible
> *
> * This function allocates a page from the kernel page pool and applies
> * a NUMA policy associated with the VMA or the current process.
> @@ -2021,7 +2022,7 @@ static struct page *alloc_page_interleave(gfp_t gfp, unsigned order,
> */
> struct page *
> alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
> - unsigned long addr, int node)
> + unsigned long addr, int node, bool hugepage)
> {
> struct mempolicy *pol;
> struct page *page;
> @@ -2039,6 +2040,31 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
> goto out;
> }
>
> + if (unlikely(IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && hugepage)) {
> + int hpage_node = node;
> +
> + /*
> + * For hugepage allocation and non-interleave policy which
> + * allows the current node (or other explicitly preferred
> + * node) we only try to allocate from the current/preferred
> + * node and don't fall back to other nodes, as the cost of
> + * remote accesses would likely offset THP benefits.
> + *
> + * If the policy is interleave, or does not allow the current
> + * node in its nodemask, we allocate the standard way.
> + */
> + if (pol->mode == MPOL_PREFERRED && !(pol->flags & MPOL_F_LOCAL))
> + hpage_node = pol->v.preferred_node;
> +
> + nmask = policy_nodemask(gfp, pol);
> + if (!nmask || node_isset(hpage_node, *nmask)) {
> + mpol_cond_put(pol);
> + page = __alloc_pages_node(hpage_node,
> + gfp | __GFP_THISNODE, order);
> + goto out;
> + }
> + }
> +
> nmask = policy_nodemask(gfp, pol);
> preferred_nid = policy_node(gfp, pol, node);
> page = __alloc_pages_nodemask(gfp, order, preferred_nid, nmask);
> diff --git a/mm/shmem.c b/mm/shmem.c
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1439,7 +1439,7 @@ static struct page *shmem_alloc_hugepage(gfp_t gfp,
>
> shmem_pseudo_vma_init(&pvma, info, hindex);
> page = alloc_pages_vma(gfp | __GFP_COMP | __GFP_NORETRY | __GFP_NOWARN,
> - HPAGE_PMD_ORDER, &pvma, 0, numa_node_id());
> + HPAGE_PMD_ORDER, &pvma, 0, numa_node_id(), true);
> shmem_pseudo_vma_destroy(&pvma);
> if (page)
> prep_transhuge_page(page);

--
Michal Hocko
SUSE Labs

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