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Commit a7a52a19 authored by Linux Build Service Account's avatar Linux Build Service Account Committed by Gerrit - the friendly Code Review server
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Merge "mm: disable fault around on emulated access bit architecture"

parents f7a398ff e3b714ab

Documentation/sysctl/vm.txt

+22 −0
Original line number Diff line number Diff line
@@ -64,6 +64,7 @@ Currently, these files are in /proc/sys/vm: 
- vfs_cache_pressure

- watermark_scale_factor

- zone_reclaim_mode

- want_old_faultaround_pte



==============================================================
@@ -891,4 +892,25 @@ Allowing regular swap effectively restricts allocations to the local 
node unless explicitly overridden by memory policies or cpuset

configurations.



=============================================================



want_old_faultaround_pte:



By default faultaround code produces young pte. When want_old_faultaround_pte is

set to 1, faultaround produces old ptes.



During sparse file access faultaround gets more pages mapped and when all of

them are young (default), under memory pressure, this makes vmscan swap out anon

pages instead, or to drop other page cache pages which otherwise stay resident.

Setting want_old_faultaround_pte to 1 avoids this.



Making the faultaround ptes old can result in performance regression on some

architectures. This is due to cycles spent in micro-faults which would take page

walk to set young bit in the pte. One such known test that shows a regression on

x86 is unixbench shell8. Set want_old_faultaround_pte to 1 on architectures

which does not show this regression or if the workload shows overall performance

benefit with old faultaround ptes.



The default value is 0.



============ End of Document =================================

include/linux/mm.h

+4 −0
Original line number Diff line number Diff line
@@ -286,6 +286,7 @@ extern pgprot_t protection_map[16]; 
#define FAULT_FLAG_INSTRUCTION  0x100	/* The fault was during an instruction fetch */

/* Speculative fault, not holding mmap_sem */

#define FAULT_FLAG_SPECULATIVE	0x200

#define FAULT_FLAG_PREFAULT_OLD 0x400   /* Make faultaround ptes old */



/*

 * vm_fault is filled by the the pagefault handler and passed to the vma's
@@ -323,6 +324,7 @@ struct vm_fault { 
struct fault_env {

	struct vm_area_struct *vma;	/* Target VMA */

	unsigned long address;		/* Faulting virtual address */

	unsigned long fault_address;    /* Saved faulting virtual address */

	unsigned int flags;		/* FAULT_FLAG_xxx flags */

	pmd_t *pmd;			/* Pointer to pmd entry matching

					 * the 'address'
@@ -2584,6 +2586,8 @@ void __init setup_nr_node_ids(void); 
static inline void setup_nr_node_ids(void) {}

#endif



extern int want_old_faultaround_pte;



#ifdef CONFIG_PROCESS_RECLAIM

struct reclaim_param {

	struct vm_area_struct *vma;

kernel/sysctl.c

+9 −0
Original line number Diff line number Diff line
@@ -1486,6 +1486,15 @@ static struct ctl_table vm_table[] = { 
		.extra1		= &zero,

		.extra2		= &one_hundred,

	},

	{

		.procname       = "want_old_faultaround_pte",

		.data           = &want_old_faultaround_pte,

		.maxlen         = sizeof(want_old_faultaround_pte),

		.mode           = 0644,

		.proc_handler   = proc_dointvec_minmax,

		.extra1         = &zero,

		.extra2         = &one,

	},

#ifdef CONFIG_HUGETLB_PAGE

	{

		.procname	= "nr_hugepages",

mm/filemap.c

+10 −0
Original line number Diff line number Diff line
@@ -47,6 +47,8 @@ 


#include <asm/mman.h>



int want_old_faultaround_pte = 1;



/*

 * Shared mappings implemented 30.11.1994. It's not fully working yet,

 * though.
@@ -2287,6 +2289,14 @@ void filemap_map_pages(struct fault_env *fe, 
		if (fe->pte)

			fe->pte += iter.index - last_pgoff;

		last_pgoff = iter.index;



		if (want_old_faultaround_pte) {

			if (fe->address == fe->fault_address)

				fe->flags &= ~FAULT_FLAG_PREFAULT_OLD;

			else

				fe->flags |= FAULT_FLAG_PREFAULT_OLD;

		}



		if (alloc_set_pte(fe, NULL, page))

			goto unlock;

		unlock_page(page);

mm/memory.c

+13 −0
Original line number Diff line number Diff line
@@ -3212,6 +3212,10 @@ int alloc_set_pte(struct fault_env *fe, struct mem_cgroup *memcg, 
	entry = mk_pte(page, fe->vma_page_prot);

	if (write)

		entry = maybe_mkwrite(pte_mkdirty(entry), fe->vma_flags);



	if (fe->flags & FAULT_FLAG_PREFAULT_OLD)

		entry = pte_mkold(entry);



	/* copy-on-write page */

	if (write && !(fe->vma_flags & VM_SHARED)) {

		inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
@@ -3230,8 +3234,16 @@ int alloc_set_pte(struct fault_env *fe, struct mem_cgroup *memcg, 
	return 0;

}



/*

 * If architecture emulates "accessed" or "young" bit without HW support,

 * there is no much gain with fault_around.

 */

static unsigned long fault_around_bytes __read_mostly =

#ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS

	PAGE_SIZE;

#else

	rounddown_pow_of_two(65536);

#endif



#ifdef CONFIG_DEBUG_FS

static int fault_around_bytes_get(void *data, u64 *val)
@@ -3300,6 +3312,7 @@ static int do_fault_around(struct fault_env *fe, pgoff_t start_pgoff) 
	pgoff_t end_pgoff;

	int off, ret = 0;



	fe->fault_address = address;

	nr_pages = READ_ONCE(fault_around_bytes) >> PAGE_SHIFT;

	mask = ~(nr_pages * PAGE_SIZE - 1) & PAGE_MASK;