Re: [PATCH 3/7] mm: rework __isolate_lru_page() file/anon filter

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Konstantin Khlebnikov wrote:
Hugh Dickins wrote:
On Wed, 29 Feb 2012, Konstantin Khlebnikov wrote:

This patch adds file/anon filter bits into isolate_mode_t,
this allows to simplify checks in __isolate_lru_page().

Signed-off-by: Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx>

Almost-Acked-by: Hugh Dickins<hughd@xxxxxxxxxx>

with one whitespace nit, and one functional addition requested.

I'm perfectly happy with your :?s myself, but some people do dislike
them.  I'm happy with the switch alternative if it's as efficient:
something that surprised me very much when trying to get convincing
performance numbers for per-memcg per-zone lru_lock at home...

... __isolate_lru_page() featured astonishly high on the perf report
of streaming from files on ext4 on /dev/ram0 to /dev/null, coming
immediately below the obvious zeroing and copying: okay, the zeroing
and copying were around 30% each, and __isolate_lru_page() down around
2% or below, but even so it seemed very odd that it should feature so
high, and any optimizations to it very welcome - unless it was purely
some bogus result.

Actually ANON/FILE ACTIVE/INACTIVE checks does not required at non-lumpy reclaim
(all pages are picked from right lru list) and compaction (it does not care).
But seems like removing these two bit-checks cannot give noticeable performance gain.

This patch can be postponed. It does not so important and
it does not share context with other patches in this set.

Oops, no it cannot be dropped. Next patch "mm: push lru index into shrink_[in]active_list()"
kills "file" variable in isolate_lru_pages(). I sent v2 for this patch only.



---
   include/linux/mmzone.h |    4 ++++
   include/linux/swap.h   |    2 +-
   mm/compaction.c        |    5 +++--
   mm/vmscan.c            |   27 +++++++++++++--------------
   4 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index eff4918..2fed935 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -193,6 +193,10 @@ struct lruvec {
   #define ISOLATE_UNMAPPED	((__force isolate_mode_t)0x8)
   /* Isolate for asynchronous migration */
   #define ISOLATE_ASYNC_MIGRATE	((__force isolate_mode_t)0x10)
+/* Isolate swap-backed pages */
+#define	ISOLATE_ANON		((__force isolate_mode_t)0x20)
+/* Isolate file-backed pages */
+#define	ISOLATE_FILE		((__force isolate_mode_t)0x40)

   From the patch you can see that the #defines above yours used a
space where you have used a tab: better to use a space as above.

@@ -375,7 +376,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
   			mode |= ISOLATE_ASYNC_MIGRATE;

   		/* Try isolate the page */
-		if (__isolate_lru_page(page, mode, 0) != 0)
+		if (__isolate_lru_page(page, mode) != 0)
   			continue;

I thought you were missing something there, but no, that's rather
the case you are simplifying.  However...

diff --git a/mm/vmscan.c b/mm/vmscan.c
index af6cfe7..1b70338 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1520,6 +1511,10 @@ shrink_inactive_list(unsigned long nr_to_scan, struct mem_cgroup_zone *mz,
   		isolate_mode |= ISOLATE_UNMAPPED;
   	if (!sc->may_writepage)
   		isolate_mode |= ISOLATE_CLEAN;
+	if (file)
+		isolate_mode |= ISOLATE_FILE;
+	else
+		isolate_mode |= ISOLATE_ANON;

Above here, under "if (sc->reclaim_mode&   RECLAIM_MODE_LUMPYRECLAIM)",
don't you need

		isolate_mode |= ISOLATE_ACTIVE | ISOLATE_FILE | ISOLATE_ANON;

now to reproduce the same "all_lru_mode" behaviour as before?

Yes, I missed this. Thanks.


Hugh

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