[v4] mm,thp,shmem: limit shmem THP alloc gfp_mask
diff mbox series

Message ID 20201023204804.3f8d19c1@imladris.surriel.com
State In Next
Commit 89747bc8a6501e889c4b1abb761db82cff1b0676
Headers show
Series
  • [v4] mm,thp,shmem: limit shmem THP alloc gfp_mask
Related show

Commit Message

Rik van Riel Oct. 24, 2020, 12:48 a.m. UTC
The allocation flags of anonymous transparent huge pages can be controlled
through the files in /sys/kernel/mm/transparent_hugepage/defrag, which can
help the system from getting bogged down in the page reclaim and compaction
code when many THPs are getting allocated simultaneously.

However, the gfp_mask for shmem THP allocations were not limited by those
configuration settings, and some workloads ended up with all CPUs stuck
on the LRU lock in the page reclaim code, trying to allocate dozens of
THPs simultaneously.

This patch applies the same configurated limitation of THPs to shmem
hugepage allocations, to prevent that from happening.

This way a THP defrag setting of "never" or "defer+madvise" will result
in quick allocation failures without direct reclaim when no 2MB free
pages are available.

With this patch applied, THP allocations for tmpfs will be a little
more aggressive than today for files mmapped with MADV_HUGEPAGE,
and a little less aggressive for files that are not mmapped or
mapped without that flag.

Signed-off-by: Rik van Riel <riel@surriel.com>
--- 
v4: rename alloc_hugepage_direct_gfpmask to vma_thp_gfp_mask (Matthew Wilcox)
v3: fix NULL vma issue spotted by Hugh Dickins & tested
v2: move gfp calculation to shmem_getpage_gfp as suggested by Yu Xu

Comments

Matthew Wilcox Oct. 24, 2020, 2:09 a.m. UTC | #1
On Fri, Oct 23, 2020 at 08:48:04PM -0400, Rik van Riel wrote:
> The allocation flags of anonymous transparent huge pages can be controlled
> through the files in /sys/kernel/mm/transparent_hugepage/defrag, which can
> help the system from getting bogged down in the page reclaim and compaction
> code when many THPs are getting allocated simultaneously.
> 
> However, the gfp_mask for shmem THP allocations were not limited by those
> configuration settings, and some workloads ended up with all CPUs stuck
> on the LRU lock in the page reclaim code, trying to allocate dozens of
> THPs simultaneously.
> 
> This patch applies the same configurated limitation of THPs to shmem
> hugepage allocations, to prevent that from happening.
> 
> This way a THP defrag setting of "never" or "defer+madvise" will result
> in quick allocation failures without direct reclaim when no 2MB free
> pages are available.
> 
> With this patch applied, THP allocations for tmpfs will be a little
> more aggressive than today for files mmapped with MADV_HUGEPAGE,
> and a little less aggressive for files that are not mmapped or
> mapped without that flag.

How about this code path though?

shmem_get_pages() [ in i915 ]
  shmem_read_mapping_page_gfp(__GFP_NORETRY | __GFP_NOWARN)
    shmem_getpage_gfp()
      shmem_alloc_and_acct_page()
        shmem_alloc_hugepage()

I feel like the NORETRY from i915 should override whatever is set
in sysfs for anon THPs.  What do others think?

> Signed-off-by: Rik van Riel <riel@surriel.com>
> --- 
> v4: rename alloc_hugepage_direct_gfpmask to vma_thp_gfp_mask (Matthew Wilcox)
> v3: fix NULL vma issue spotted by Hugh Dickins & tested
> v2: move gfp calculation to shmem_getpage_gfp as suggested by Yu Xu
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index c603237e006c..c7615c9ba03c 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -614,6 +614,8 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask);
>  extern void pm_restrict_gfp_mask(void);
>  extern void pm_restore_gfp_mask(void);
>  
> +extern gfp_t vma_thp_gfp_mask(struct vm_area_struct *vma);
> +
>  #ifdef CONFIG_PM_SLEEP
>  extern bool pm_suspended_storage(void);
>  #else
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 9474dbc150ed..c5d03b2f2f2f 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -649,9 +649,9 @@ 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)
> +gfp_t vma_thp_gfp_mask(struct vm_area_struct *vma)
>  {
> -	const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
> +	const bool vma_madvised = vma && (vma->vm_flags & VM_HUGEPAGE);
>  
>  	/* Always do synchronous compaction */
>  	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
> @@ -744,7 +744,7 @@ 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 = vma_thp_gfp_mask(vma);
>  	page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
>  	if (unlikely(!page)) {
>  		count_vm_event(THP_FAULT_FALLBACK);
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 537c137698f8..6c3cb192a88d 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1545,8 +1545,8 @@ static struct page *shmem_alloc_hugepage(gfp_t gfp,
>  		return NULL;
>  
>  	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(), true);
> +	page = alloc_pages_vma(gfp, HPAGE_PMD_ORDER, &pvma, 0, numa_node_id(),
> +			       true);
>  	shmem_pseudo_vma_destroy(&pvma);
>  	if (page)
>  		prep_transhuge_page(page);
> @@ -1802,6 +1802,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
>  	struct page *page;
>  	enum sgp_type sgp_huge = sgp;
>  	pgoff_t hindex = index;
> +	gfp_t huge_gfp;
>  	int error;
>  	int once = 0;
>  	int alloced = 0;
> @@ -1887,7 +1888,8 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
>  	}
>  
>  alloc_huge:
> -	page = shmem_alloc_and_acct_page(gfp, inode, index, true);
> +	huge_gfp = vma_thp_gfp_mask(vma);
> +	page = shmem_alloc_and_acct_page(huge_gfp, inode, index, true);
>  	if (IS_ERR(page)) {
>  alloc_nohuge:
>  		page = shmem_alloc_and_acct_page(gfp, inode,
Rik van Riel Oct. 24, 2020, 5:53 p.m. UTC | #2
On Sat, 2020-10-24 at 03:09 +0100, Matthew Wilcox wrote:
> On Fri, Oct 23, 2020 at 08:48:04PM -0400, Rik van Riel wrote:
> > The allocation flags of anonymous transparent huge pages can be
> > controlled
> > through the files in /sys/kernel/mm/transparent_hugepage/defrag,
> > which can
> > help the system from getting bogged down in the page reclaim and
> > compaction
> > code when many THPs are getting allocated simultaneously.
> > 
> > However, the gfp_mask for shmem THP allocations were not limited by
> > those
> > configuration settings, and some workloads ended up with all CPUs
> > stuck
> > on the LRU lock in the page reclaim code, trying to allocate dozens
> > of
> > THPs simultaneously.
> > 
> > This patch applies the same configurated limitation of THPs to
> > shmem
> > hugepage allocations, to prevent that from happening.
> > 
> > This way a THP defrag setting of "never" or "defer+madvise" will
> > result
> > in quick allocation failures without direct reclaim when no 2MB
> > free
> > pages are available.
> > 
> > With this patch applied, THP allocations for tmpfs will be a little
> > more aggressive than today for files mmapped with MADV_HUGEPAGE,
> > and a little less aggressive for files that are not mmapped or
> > mapped without that flag.
> 
> How about this code path though?
> 
> shmem_get_pages() [ in i915 ]
>   shmem_read_mapping_page_gfp(__GFP_NORETRY | __GFP_NOWARN)
>     shmem_getpage_gfp()
>       shmem_alloc_and_acct_page()
>         shmem_alloc_hugepage()
> 
> I feel like the NORETRY from i915 should override whatever is set
> in sysfs for anon THPs.  What do others think?

It looks like currently the only way to get a THP
allocation with __GFP_DIRECT_RECLAIM and without
__GFP_NORETRY (which does nothing without
__GFP_DIRECT_RECLAIM) is to explicitly do an
madvise MADV_HUGEPAGE on a VMA.

I am not convinced the i915 driver should
override a userspace madvise.

Patch
diff mbox series

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index c603237e006c..c7615c9ba03c 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -614,6 +614,8 @@  bool gfp_pfmemalloc_allowed(gfp_t gfp_mask);
 extern void pm_restrict_gfp_mask(void);
 extern void pm_restore_gfp_mask(void);
 
+extern gfp_t vma_thp_gfp_mask(struct vm_area_struct *vma);
+
 #ifdef CONFIG_PM_SLEEP
 extern bool pm_suspended_storage(void);
 #else
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9474dbc150ed..c5d03b2f2f2f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -649,9 +649,9 @@  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)
+gfp_t vma_thp_gfp_mask(struct vm_area_struct *vma)
 {
-	const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
+	const bool vma_madvised = vma && (vma->vm_flags & VM_HUGEPAGE);
 
 	/* Always do synchronous compaction */
 	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
@@ -744,7 +744,7 @@  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 = vma_thp_gfp_mask(vma);
 	page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
 	if (unlikely(!page)) {
 		count_vm_event(THP_FAULT_FALLBACK);
diff --git a/mm/shmem.c b/mm/shmem.c
index 537c137698f8..6c3cb192a88d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1545,8 +1545,8 @@  static struct page *shmem_alloc_hugepage(gfp_t gfp,
 		return NULL;
 
 	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(), true);
+	page = alloc_pages_vma(gfp, HPAGE_PMD_ORDER, &pvma, 0, numa_node_id(),
+			       true);
 	shmem_pseudo_vma_destroy(&pvma);
 	if (page)
 		prep_transhuge_page(page);
@@ -1802,6 +1802,7 @@  static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
 	struct page *page;
 	enum sgp_type sgp_huge = sgp;
 	pgoff_t hindex = index;
+	gfp_t huge_gfp;
 	int error;
 	int once = 0;
 	int alloced = 0;
@@ -1887,7 +1888,8 @@  static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
 	}
 
 alloc_huge:
-	page = shmem_alloc_and_acct_page(gfp, inode, index, true);
+	huge_gfp = vma_thp_gfp_mask(vma);
+	page = shmem_alloc_and_acct_page(huge_gfp, inode, index, true);
 	if (IS_ERR(page)) {
 alloc_nohuge:
 		page = shmem_alloc_and_acct_page(gfp, inode,