Re: [PATCH 2/2] mm/dax: Don't enable huge dax mapping by default
From: Jan Kara <jack@suse.cz>
Date: 2019-02-28 09:40:16
Also in:
linux-mm, lkml
On Thu 28-02-19 14:05:22, Aneesh Kumar K.V wrote:
Add a flag to indicate the ability to do huge page dax mapping. On architecture like ppc64, the hypervisor can disable huge page support in the guest. In such a case, we should not enable huge page dax mapping. This patch adds a flag which the architecture code will update to indicate huge page dax mapping support. Architectures mostly do transparent_hugepage_flag = 0; if they can't do hugepages. That also takes care of disabling dax hugepage mapping with this change. Without this patch we get the below error with kvm on ppc64. [ 118.849975] lpar: Failed hash pte insert with error -4 NOTE: The patch also use echo never > /sys/kernel/mm/transparent_hugepage/enabled to disable dax huge page mapping. Signed-off-by: Aneesh Kumar K.V <redacted>
Added Dan to CC for opinion. I kind of fail to see why you don't use TRANSPARENT_HUGEPAGE_FLAG for this. I know that technically DAX huge pages and normal THPs are different things but so far we've tried to avoid making that distinction visible to userspace. Honza
quoted hunk ↗ jump to hunk
--- TODO: * Add Fixes: tag include/linux/huge_mm.h | 4 +++- mm/huge_memory.c | 4 ++++ 2 files changed, 7 insertions(+), 1 deletion(-)diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index 381e872bfde0..01ad5258545e 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h@@ -53,6 +53,7 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr, pud_t *pud, pfn_t pfn, bool write); enum transparent_hugepage_flag { TRANSPARENT_HUGEPAGE_FLAG, + TRANSPARENT_HUGEPAGE_DAX_FLAG, TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,@@ -111,7 +112,8 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma) if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_FLAG)) return true; - if (vma_is_dax(vma)) + if (vma_is_dax(vma) && + (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_DAX_FLAG))) return true; if (transparent_hugepage_flags &diff --git a/mm/huge_memory.c b/mm/huge_memory.c index faf357eaf0ce..43d742fe0341 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c@@ -53,6 +53,7 @@ unsigned long transparent_hugepage_flags __read_mostly = #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)| #endif + (1 << TRANSPARENT_HUGEPAGE_DAX_FLAG) | (1<<TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG)| (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)| (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);@@ -475,6 +476,8 @@ static int __init setup_transparent_hugepage(char *str) &transparent_hugepage_flags); clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags); + clear_bit(TRANSPARENT_HUGEPAGE_DAX_FLAG, + &transparent_hugepage_flags); ret = 1; } out:@@ -753,6 +756,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, spinlock_t *ptl; ptl = pmd_lock(mm, pmd); + /* should we check for none here again? */ entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); if (pfn_t_devmap(pfn)) entry = pmd_mkdevmap(entry);-- 2.20.1
-- Jan Kara [off-list ref] SUSE Labs, CR