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mm: numa: cleanup flow of transhuge page migration

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When correcting commit 04fa5d6a65 ("mm: migrate: check page_count of
THP before migrating") Hugh Dickins noted that the control flow for
transhuge migration was difficult to follow.  Unconditionally calling
put_page() in numamigrate_isolate_page() made the failure paths of both
migrate_misplaced_transhuge_page() and migrate_misplaced_page() more
complex that they should be.  Further, he was extremely wary that an
unlock_page() should ever happen after a put_page() even if the
put_page() should never be the final put_page.

Hugh implemented the following cleanup to simplify the path by calling
putback_lru_page() inside numamigrate_isolate_page() if it failed to
isolate and always calling unlock_page() within
migrate_misplaced_transhuge_page().

There is no functional change after this patch is applied but the code
is easier to follow and unlock_page() always happens before put_page().

[mgorman@suse.de: changelog only]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Simon Jeons <simon.jeons@gmail.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins
2013-02-22 16:34:33 -08:00
committed by Linus Torvalds
parent 75980e97da
commit 340ef3902c
2 changed files with 54 additions and 73 deletions
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28
mm/huge_memory.c
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@@ -1296,7 +1296,6 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
int target_nid;
int current_nid = -1;
bool migrated;
bool page_locked = false;
spin_lock(&mm->page_table_lock);
if (unlikely(!pmd_same(pmd, *pmdp)))
@@ -1318,7 +1317,6 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
/* Acquire the page lock to serialise THP migrations */
spin_unlock(&mm->page_table_lock);
lock_page(page);
page_locked = true;
/* Confirm the PTE did not while locked */
spin_lock(&mm->page_table_lock);
@@ -1331,34 +1329,26 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
/* Migrate the THP to the requested node */
migrated = migrate_misplaced_transhuge_page(mm, vma,
pmdp, pmd, addr,
page, target_nid);
if (migrated)
current_nid = target_nid;
else {
spin_lock(&mm->page_table_lock);
if (unlikely(!pmd_same(pmd, *pmdp))) {
unlock_page(page);
goto out_unlock;
}
goto clear_pmdnuma;
}
pmdp, pmd, addr, page, target_nid);
if (!migrated)
goto check_same;
task_numa_fault(current_nid, HPAGE_PMD_NR, migrated);
task_numa_fault(target_nid, HPAGE_PMD_NR, true);
return 0;
check_same:
spin_lock(&mm->page_table_lock);
if (unlikely(!pmd_same(pmd, *pmdp)))
goto out_unlock;
clear_pmdnuma:
pmd = pmd_mknonnuma(pmd);
set_pmd_at(mm, haddr, pmdp, pmd);
VM_BUG_ON(pmd_numa(*pmdp));
update_mmu_cache_pmd(vma, addr, pmdp);
if (page_locked)
unlock_page(page);
out_unlock:
spin_unlock(&mm->page_table_lock);
if (current_nid != -1)
task_numa_fault(current_nid, HPAGE_PMD_NR, migrated);
task_numa_fault(current_nid, HPAGE_PMD_NR, false);
return 0;
}