Hello, it's too late since I sent previos patch.
https://lkml.org/lkml/2015/6/3/37
This patch is alomost new compared to previos approach.
I think this is more simple, clear and easy to review.
One thing I should notice is that I have tested this patch
and couldn't find any critical problem so I rebased patchset
onto recent mmotm(ie, mmotm-2015-10-15-15-20) to send formal
patchset. Unfortunately, I start to see sudden discarding of
the page we shouldn't do. IOW, application's valid anonymous page
was disappeared suddenly.
When I look through THP changes, I think we could lose
dirty bit of pte between freeze_page and unfreeze_page
when we mark it as migration entry and restore it.
So, I added below simple code without enough considering
and cannot see the problem any more.
I hope it's good hint to find right fix this problem.
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d5ea516ffb54..e881c04f5950 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3138,6 +3138,9 @@ static void unfreeze_page_vma(struct vm_area_struct *vma,
struct page *page,
if (is_write_migration_entry(swp_entry))
entry = maybe_mkwrite(entry, vma);
+ if (PageDirty(page))
+ SetPageDirty(page);
+
flush_dcache_page(page);
set_pte_at(vma->vm_mm, address, pte + i, entry);
Although it fixes abvove problem, I can encounter below another bug
in several hours.
BUG: Bad rss-counter state mm:ffff88007fc28000 idx:1 val:439
BUG: Bad rss-counter state mm:ffff88007fc28000 idx:2 val:73
Or
BUG: Bad rss-counter state mm:ffff88007fc28000 idx:1 val:512
It seems we are zapping THP page without decreasing MM_ANONPAGES
and MM_SWAPENTS. Of course, it could be a bug of MADV_FREE and
recent changes of THP reveals it. What I can say is I couldn't see
any problem until mmotm-2015-10-06-16-30 so I guess there is some
conflict with THP-refcount redesign of Kirill or it makes to reveal
MADV_FREE's hidden bug.
I will hunt it down but I hope Kirill might catch it up earlier than me.
Major thing with this patch is two things.
1. Work with MADV_FREE on PG_dirty page.
So far, MADV_FREE doesn't work with page which is not in swap cache
but has PG_dirty(ex, swapped-in page). Details are in [3/5].
2. Make MADV_FREE discard path simple
Current logic for discarding hinted page is really mess
so [4/5] makes it simple and clean.
3. Fix with KSM page
A process can have KSM page which is no dirty bit in page table
entry and no PG_dirty in page->flags so VM could discard it wrongly.
[5/5] fixes it.
Minchan Kim (5):
[1/5] mm: MADV_FREE trivial clean up
[2/5] mm: skip huge zero page in MADV_FREE
[3/5] mm: clear PG_dirty to mark page freeable
[4/5] mm: simplify reclaim path for MADV_FREE
[5/5] mm: mark stable page dirty in KSM
include/linux/rmap.h | 6 +----
mm/huge_memory.c | 9 ++++----
mm/ksm.c | 12 ++++++++++
mm/madvise.c | 29 +++++++++++-------------
mm/rmap.c | 46 +++++++------------------------------
mm/swap_state.c | 5 ++--
mm/vmscan.c | 64 ++++++++++++++++------------------------------------
7 files changed, 60 insertions(+), 111 deletions(-)
--
1.9.1
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