Re: [PATCH -v3 07/10] mm, THP, swap: Support to add/delete THP to/from swap cache

Hi, Anshuman,

Thanks for comments!

Anshuman Khandual [off-list ref] writes:

On 09/07/2016 10:16 PM, Huang, Ying wrote:

quoted

From: Huang Ying <redacted>

With this patch, a THP (Transparent Huge Page) can be added/deleted
to/from the swap cache as a set of sub-pages (512 on x86_64).

This will be used for the THP (Transparent Huge Page) swap support.
Where one THP may be added/delted to/from the swap cache.  This will
batch the swap cache operations to reduce the lock acquire/release times
for the THP swap too.

Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <redacted>
Cc: Andrea Arcangeli <redacted>
Cc: Kirill A. Shutemov <redacted>
Signed-off-by: "Huang, Ying" <redacted>
---
 include/linux/page-flags.h |  2 +-
 mm/swap_state.c            | 57 +++++++++++++++++++++++++++++++---------------
 2 files changed, 40 insertions(+), 19 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 74e4dda..f5bcbea 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h

@@ -314,7 +314,7 @@ PAGEFLAG_FALSE(HighMem)
 #endif
 
 #ifdef CONFIG_SWAP
-PAGEFLAG(SwapCache, swapcache, PF_NO_COMPOUND)
+PAGEFLAG(SwapCache, swapcache, PF_NO_TAIL)

What is the reason for this change ? The commit message does not seem
to explain.

Before this change, SetPageSwapCache() cannot be called for THP, after
the change, SetPageSwapCache() could be called for the head page of the
THP, but not the tail pages.  Because we will never do that before this
patch series.

Best Regards,
Huang, Ying

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