Re: [PATCH v4 4/4] mm: introduce MADV_PAGEOUT

Minchan Kim
2019-07-12T05:18:39Z

Hi Johannes,

On Thu, Jul 11, 2019 at 02:42:23PM -0400, Johannes Weiner wrote:
> On Thu, Jul 11, 2019 at 10:25:28AM +0900, Minchan Kim wrote:
> > @@ -480,6 +482,198 @@ static long madvise_cold(struct vm_area_struct *vma,
> > return 0;
> > }
> >
> > +static int madvise_pageout_pte_range(pmd_t *pmd, unsigned long addr,
> > + unsigned long end, struct mm_walk *walk)
> > +{
> > + struct mmu_gather *tlb = walk->private;
> > + struct mm_struct *mm = tlb->mm;
> > + struct vm_area_struct *vma = walk->vma;
> > + pte_t *orig_pte, *pte, ptent;
> > + spinlock_t *ptl;
> > + LIST_HEAD(page_list);
> > + struct page *page;
> > + unsigned long next;
> > +
> > + if (fatal_signal_pending(current))
> > + return -EINTR;
> > +
> > + next = pmd_addr_end(addr, end);
> > + if (pmd_trans_huge(*pmd)) {
> > + pmd_t orig_pmd;
> > +
> > + tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
> > + ptl = pmd_trans_huge_lock(pmd, vma);
> > + if (!ptl)
> > + return 0;
> > +
> > + orig_pmd = *pmd;
> > + if (is_huge_zero_pmd(orig_pmd))
> > + goto huge_unlock;
> > +
> > + if (unlikely(!pmd_present(orig_pmd))) {
> > + VM_BUG_ON(thp_migration_supported() &&
> > + !is_pmd_migration_entry(orig_pmd));
> > + goto huge_unlock;
> > + }
> > +
> > + page = pmd_page(orig_pmd);
> > + if (next - addr != HPAGE_PMD_SIZE) {
> > + int err;
> > +
> > + if (page_mapcount(page) != 1)
> > + goto huge_unlock;
> > + get_page(page);
> > + spin_unlock(ptl);
> > + lock_page(page);
> > + err = split_huge_page(page);
> > + unlock_page(page);
> > + put_page(page);
> > + if (!err)
> > + goto regular_page;
> > + return 0;
> > + }
> > +
> > + if (isolate_lru_page(page))
> > + goto huge_unlock;
> > +
> > + if (pmd_young(orig_pmd)) {
> > + pmdp_invalidate(vma, addr, pmd);
> > + orig_pmd = pmd_mkold(orig_pmd);
> > +
> > + set_pmd_at(mm, addr, pmd, orig_pmd);
> > + tlb_remove_tlb_entry(tlb, pmd, addr);
> > + }
> > +
> > + ClearPageReferenced(page);
> > + test_and_clear_page_young(page);
> > + list_add(&page->lru, &page_list);
> > +huge_unlock:
> > + spin_unlock(ptl);
> > + reclaim_pages(&page_list);
> > + return 0;
> > + }
> > +
> > + if (pmd_trans_unstable(pmd))
> > + return 0;
> > +regular_page:
> > + tlb_change_page_size(tlb, PAGE_SIZE);
> > + orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> > + flush_tlb_batched_pending(mm);
> > + arch_enter_lazy_mmu_mode();
> > + for (; addr < end; pte++, addr += PAGE_SIZE) {
> > + ptent = *pte;
> > + if (!pte_present(ptent))
> > + continue;
> > +
> > + page = vm_normal_page(vma, addr, ptent);
> > + if (!page)
> > + continue;
> > +
> > + /*
> > + * creating a THP page is expensive so split it only if we
> > + * are sure it's worth. Split it if we are only owner.
> > + */
> > + if (PageTransCompound(page)) {
> > + if (page_mapcount(page) != 1)
> > + break;
> > + get_page(page);
> > + if (!trylock_page(page)) {
> > + put_page(page);
> > + break;
> > + }
> > + pte_unmap_unlock(orig_pte, ptl);
> > + if (split_huge_page(page)) {
> > + unlock_page(page);
> > + put_page(page);
> > + pte_offset_map_lock(mm, pmd, addr, &ptl);
> > + break;
> > + }
> > + unlock_page(page);
> > + put_page(page);
> > + pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
> > + pte--;
> > + addr -= PAGE_SIZE;
> > + continue;
> > + }
> > +
> > + VM_BUG_ON_PAGE(PageTransCompound(page), page);
> > +
> > + if (isolate_lru_page(page))
> > + continue;
> > +
> > + if (pte_young(ptent)) {
> > + ptent = ptep_get_and_clear_full(mm, addr, pte,
> > + tlb->fullmm);
> > + ptent = pte_mkold(ptent);
> > + set_pte_at(mm, addr, pte, ptent);
> > + tlb_remove_tlb_entry(tlb, pte, addr);
> > + }
> > + ClearPageReferenced(page);
> > + test_and_clear_page_young(page);
> > + list_add(&page->lru, &page_list);
> > + }
> > +
> > + arch_leave_lazy_mmu_mode();
> > + pte_unmap_unlock(orig_pte, ptl);
> > + reclaim_pages(&page_list);
> > + cond_resched();
> > +
> > + return 0;
> > +}
>
> I know you have briefly talked about code sharing already.
>
> While I agree that sharing with MADV_FREE is maybe a stretch, I
> applied these patches and compared the pageout and the cold page table
> functions, and they are line for line the same EXCEPT for 2-3 lines at
> the very end, where one reclaims and the other deactivates. It would
> be good to share here, it shouldn't be hard or result in fragile code.

Fair enough if we leave MADV_FREE.

>
> Something like int madvise_cold_or_pageout_range(..., bool pageout)?

How about this?

From 41592f23e876ec21e49dc3c76dc89538e2bb16be Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Fri, 12 Jul 2019 14:05:36 +0900
Subject: [PATCH] mm: factor out common parts between MADV_COLD and
MADV_PAGEOUT

There are many common parts between MADV_COLD and MADV_PAGEOUT.
This patch factor them out to save code duplication.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
mm/madvise.c | 201 +++++++++++++--------------------------------------
1 file changed, 52 insertions(+), 149 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index bc2f0138982e..3d3d14517cc8 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -30,6 +30,11 @@

#include "internal.h"

+struct madvise_walk_private {
+ struct mmu_gather *tlb;
+ bool pageout;
+};
+
/*
* Any behaviour which results in changes to the vma->vm_flags needs to
* take mmap_sem for writing. Others, which simply traverse vmas, need
@@ -310,16 +315,23 @@ static long madvise_willneed(struct vm_area_struct *vma,
return 0;
}

-static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,
- unsigned long end, struct mm_walk *walk)
+static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
+ unsigned long addr, unsigned long end,
+ struct mm_walk *walk)
{
- struct mmu_gather *tlb = walk->private;
+ struct madvise_walk_private *private = walk->private;
+ struct mmu_gather *tlb = private->tlb;
+ bool pageout = private->pageout;
struct mm_struct *mm = tlb->mm;
struct vm_area_struct *vma = walk->vma;
pte_t *orig_pte, *pte, ptent;
spinlock_t *ptl;
- struct page *page;
unsigned long next;
+ struct page *page = NULL;
+ LIST_HEAD(page_list);
+
+ if (fatal_signal_pending(current))
+ return -EINTR;

next = pmd_addr_end(addr, end);
if (pmd_trans_huge(*pmd)) {
@@ -358,6 +370,12 @@ static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,
return 0;
}

+ if (pageout) {
+ if (isolate_lru_page(page))
+ goto huge_unlock;
+ list_add(&page->lru, &page_list);
+ }
+
if (pmd_young(orig_pmd)) {
pmdp_invalidate(vma, addr, pmd);
orig_pmd = pmd_mkold(orig_pmd);
@@ -366,10 +384,14 @@ static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,
tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
}

+ ClearPageReferenced(page);
test_and_clear_page_young(page);
- deactivate_page(page);
huge_unlock:
spin_unlock(ptl);
+ if (pageout)
+ reclaim_pages(&page_list);
+ else
+ deactivate_page(page);
return 0;
}

@@ -423,6 +445,12 @@ static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,

VM_BUG_ON_PAGE(PageTransCompound(page), page);

+ if (pageout) {
+ if (isolate_lru_page(page))
+ continue;
+ list_add(&page->lru, &page_list);
+ }
+
if (pte_young(ptent)) {
ptent = ptep_get_and_clear_full(mm, addr, pte,
tlb->fullmm);
@@ -437,12 +465,16 @@ static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,
* As a side effect, it makes confuse idle-page tracking
* because they will miss recent referenced history.
*/
+ ClearPageReferenced(page);
test_and_clear_page_young(page);
- deactivate_page(page);
+ if (!pageout)
+ deactivate_page(page);
}

arch_enter_lazy_mmu_mode();
pte_unmap_unlock(orig_pte, ptl);
+ if (pageout)
+ reclaim_pages(&page_list);
cond_resched();

return 0;
@@ -452,10 +484,15 @@ static void madvise_cold_page_range(struct mmu_gather *tlb,
struct vm_area_struct *vma,
unsigned long addr, unsigned long end)
{
+ struct madvise_walk_private walk_private = {
+ .tlb = tlb,
+ .pageout = false,
+ };
+
struct mm_walk cold_walk = {
- .pmd_entry = madvise_cold_pte_range,
+ .pmd_entry = madvise_cold_or_pageout_pte_range,
.mm = vma->vm_mm,
- .private = tlb,
+ .private = &walk_private,
};

tlb_start_vma(tlb, vma);
@@ -482,153 +519,19 @@ static long madvise_cold(struct vm_area_struct *vma,
return 0;
}

-static int madvise_pageout_pte_range(pmd_t *pmd, unsigned long addr,
- unsigned long end, struct mm_walk *walk)
-{
- struct mmu_gather *tlb = walk->private;
- struct mm_struct *mm = tlb->mm;
- struct vm_area_struct *vma = walk->vma;
- pte_t *orig_pte, *pte, ptent;
- spinlock_t *ptl;
- LIST_HEAD(page_list);
- struct page *page;
- unsigned long next;
-
- if (fatal_signal_pending(current))
- return -EINTR;
-
- next = pmd_addr_end(addr, end);
- if (pmd_trans_huge(*pmd)) {
- pmd_t orig_pmd;
-
- tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
- ptl = pmd_trans_huge_lock(pmd, vma);
- if (!ptl)
- return 0;
-
- orig_pmd = *pmd;
- if (is_huge_zero_pmd(orig_pmd))
- goto huge_unlock;
-
- if (unlikely(!pmd_present(orig_pmd))) {
- VM_BUG_ON(thp_migration_supported() &&
- !is_pmd_migration_entry(orig_pmd));
- goto huge_unlock;
- }
-
- page = pmd_page(orig_pmd);
- if (next - addr != HPAGE_PMD_SIZE) {
- int err;
-
- if (page_mapcount(page) != 1)
- goto huge_unlock;
- get_page(page);
- spin_unlock(ptl);
- lock_page(page);
- err = split_huge_page(page);
- unlock_page(page);
- put_page(page);
- if (!err)
- goto regular_page;
- return 0;
- }
-
- if (isolate_lru_page(page))
- goto huge_unlock;
-
- if (pmd_young(orig_pmd)) {
- pmdp_invalidate(vma, addr, pmd);
- orig_pmd = pmd_mkold(orig_pmd);
-
- set_pmd_at(mm, addr, pmd, orig_pmd);
- tlb_remove_tlb_entry(tlb, pmd, addr);
- }
-
- ClearPageReferenced(page);
- test_and_clear_page_young(page);
- list_add(&page->lru, &page_list);
-huge_unlock:
- spin_unlock(ptl);
- reclaim_pages(&page_list);
- return 0;
- }
-
- if (pmd_trans_unstable(pmd))
- return 0;
-regular_page:
- tlb_change_page_size(tlb, PAGE_SIZE);
- orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
- flush_tlb_batched_pending(mm);
- arch_enter_lazy_mmu_mode();
- for (; addr < end; pte++, addr += PAGE_SIZE) {
- ptent = *pte;
- if (!pte_present(ptent))
- continue;
-
- page = vm_normal_page(vma, addr, ptent);
- if (!page)
- continue;
-
- /*
- * creating a THP page is expensive so split it only if we
- * are sure it's worth. Split it if we are only owner.
- */
- if (PageTransCompound(page)) {
- if (page_mapcount(page) != 1)
- break;
- get_page(page);
- if (!trylock_page(page)) {
- put_page(page);
- break;
- }
- pte_unmap_unlock(orig_pte, ptl);
- if (split_huge_page(page)) {
- unlock_page(page);
- put_page(page);
- pte_offset_map_lock(mm, pmd, addr, &ptl);
- break;
- }
- unlock_page(page);
- put_page(page);
- pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
- pte--;
- addr -= PAGE_SIZE;
- continue;
- }
-
- VM_BUG_ON_PAGE(PageTransCompound(page), page);
-
- if (isolate_lru_page(page))
- continue;
-
- if (pte_young(ptent)) {
- ptent = ptep_get_and_clear_full(mm, addr, pte,
- tlb->fullmm);
- ptent = pte_mkold(ptent);
- set_pte_at(mm, addr, pte, ptent);
- tlb_remove_tlb_entry(tlb, pte, addr);
- }
- ClearPageReferenced(page);
- test_and_clear_page_young(page);
- list_add(&page->lru, &page_list);
- }
-
- arch_leave_lazy_mmu_mode();
- pte_unmap_unlock(orig_pte, ptl);
- reclaim_pages(&page_list);
- cond_resched();
-
- return 0;
-}
-
static void madvise_pageout_page_range(struct mmu_gather *tlb,
struct vm_area_struct *vma,
unsigned long addr, unsigned long end)
{
+ struct madvise_walk_private walk_private = {
+ .pageout = true,
+ .tlb = tlb,
+ };
+
struct mm_walk pageout_walk = {
- .pmd_entry = madvise_pageout_pte_range,
+ .pmd_entry = madvise_cold_or_pageout_pte_range,
.mm = vma->vm_mm,
- .private = tlb,
+ .private = &walk_private,
};

tlb_start_vma(tlb, vma);
--
2.22.0.410.gd8fdbe21b5-goog