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SubjectRe: [PATCH 3/7 v2] mm: rework __isolate_lru_page() file/anon filter
On Sat, 3 Mar 2012, Konstantin Khlebnikov wrote:

> This patch adds file/anon filter bits into isolate_mode_t,
> this allows to simplify checks in __isolate_lru_page().
>
> v2:
> * use switch () instead of if ()
> * fixed lumpy-reclaim isolation mode
>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>

I'm sorry to be messing you around on this one, Konstantin, but...

(a) if you do go with the switch statements,
in kernel we align the "case"s underneath the "switch"

but

(b) I seem to be at odds with Kamezawa-san, I much preferred your
original, which did in 2 lines what the switches do in 10 lines.
And I'd say there's more opportunity for error in 10 lines than 2.

What does the compiler say (4.5.1 here, OPTIMIZE_FOR_SIZE off)?
text data bss dec hex filename
17723 113 17 17853 45bd vmscan.o.0
17671 113 17 17801 4589 vmscan.o.1
17803 113 17 17933 460d vmscan.o.2

That suggests that your v2 is the worst and your v1 the best.
Kame, can I persuade you to let the compiler decide on this?

If people have to think for a moment about the concise expression,
well, great, I don't mind people having to think about kernel code.

Hugh

> ---
> include/linux/mmzone.h | 4 ++++
> include/linux/swap.h | 2 +-
> mm/compaction.c | 5 +++--
> mm/vmscan.c | 49 +++++++++++++++++++++++++++++++-----------------
> 4 files changed, 40 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 5f1e4ee..e60dcbd 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -192,6 +192,10 @@ 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)
>
> /* LRU Isolation modes. */
> typedef unsigned __bitwise__ isolate_mode_t;
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index ba2c8d7..dc6e6a3 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -254,7 +254,7 @@ static inline void lru_cache_add_file(struct page *page)
> /* linux/mm/vmscan.c */
> extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> gfp_t gfp_mask, nodemask_t *mask);
> -extern int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file);
> +extern int __isolate_lru_page(struct page *page, isolate_mode_t mode);
> extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem,
> gfp_t gfp_mask, bool noswap);
> extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 74a8c82..cc054f7 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -261,7 +261,8 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
> unsigned long last_pageblock_nr = 0, pageblock_nr;
> unsigned long nr_scanned = 0, nr_isolated = 0;
> struct list_head *migratelist = &cc->migratepages;
> - isolate_mode_t mode = ISOLATE_ACTIVE|ISOLATE_INACTIVE;
> + isolate_mode_t mode = ISOLATE_ACTIVE | ISOLATE_INACTIVE |
> + ISOLATE_FILE | ISOLATE_ANON;
>
> /* Do not scan outside zone boundaries */
> low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
> @@ -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;
>
> VM_BUG_ON(PageTransCompound(page));
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7de3acc..cce1e14 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1029,28 +1029,35 @@ keep_lumpy:
> *
> * returns 0 on success, -ve errno on failure.
> */
> -int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file)
> +int __isolate_lru_page(struct page *page, isolate_mode_t mode)
> {
> - bool all_lru_mode;
> int ret = -EINVAL;
>
> /* Only take pages on the LRU. */
> if (!PageLRU(page))
> return ret;
>
> - all_lru_mode = (mode & (ISOLATE_ACTIVE|ISOLATE_INACTIVE)) ==
> - (ISOLATE_ACTIVE|ISOLATE_INACTIVE);
> -
> - /*
> - * When checking the active state, we need to be sure we are
> - * dealing with comparible boolean values. Take the logical not
> - * of each.
> - */
> - if (!all_lru_mode && !PageActive(page) != !(mode & ISOLATE_ACTIVE))
> - return ret;
> + switch (mode & (ISOLATE_ACTIVE | ISOLATE_INACTIVE)) {
> + case ISOLATE_ACTIVE:
> + if (!PageActive(page))
> + return ret;
> + break;
> + case ISOLATE_INACTIVE:
> + if (PageActive(page))
> + return ret;
> + break;
> + }
>
> - if (!all_lru_mode && !!page_is_file_cache(page) != file)
> - return ret;
> + switch (mode & (ISOLATE_FILE | ISOLATE_ANON)) {
> + case ISOLATE_FILE:
> + if (!page_is_file_cache(page))
> + return ret;
> + break;
> + case ISOLATE_ANON:
> + if (page_is_file_cache(page))
> + return ret;
> + break;
> + }
>
> /*
> * When this function is being called for lumpy reclaim, we
> @@ -1160,7 +1167,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>
> VM_BUG_ON(!PageLRU(page));
>
> - switch (__isolate_lru_page(page, mode, file)) {
> + switch (__isolate_lru_page(page, mode)) {
> case 0:
> mem_cgroup_lru_del(page);
> list_move(&page->lru, dst);
> @@ -1218,7 +1225,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> !PageSwapCache(cursor_page))
> break;
>
> - if (__isolate_lru_page(cursor_page, mode, file) == 0) {
> + if (__isolate_lru_page(cursor_page, mode) == 0) {
> unsigned int isolated_pages;
>
> mem_cgroup_lru_del(cursor_page);
> @@ -1503,7 +1510,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct mem_cgroup_zone *mz,
>
> set_reclaim_mode(priority, sc, false);
> if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM)
> - isolate_mode |= ISOLATE_ACTIVE;
> + isolate_mode |= ISOLATE_ACTIVE | ISOLATE_FILE | ISOLATE_ANON;
>
> lru_add_drain();
>
> @@ -1511,6 +1518,10 @@ 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;
>
> spin_lock_irq(&zone->lru_lock);
>
> @@ -1677,6 +1688,10 @@ static void shrink_active_list(unsigned long nr_to_scan,
> isolate_mode |= ISOLATE_UNMAPPED;
> if (!sc->may_writepage)
> isolate_mode |= ISOLATE_CLEAN;
> + if (file)
> + isolate_mode |= ISOLATE_FILE;
> + else
> + isolate_mode |= ISOLATE_ANON;
>
> spin_lock_irq(&zone->lru_lock);
>


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