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SubjectRe: [PATCH 2/2] mm: support MIGRATE_DISCARD
On Fri, Sep 07, 2012 at 11:24:34AM +0900, Minchan Kim wrote:
> > +unsigned long reclaim_clean_pages_from_list(struct list_head *page_list)
> > +{
> > + struct scan_control sc = {
> > + .gfp_mask = GFP_KERNEL,
> > + .priority = DEF_PRIORITY,
> > + };
> > + unsigned long ret;
> > + struct page *page, *next;
> > + LIST_HEAD(clean_pages);
> > +
> > + list_for_each_entry_safe(page, next, page_list, lru) {
> > + if (page_is_file_cache(page) && !PageDirty(page))
> > + list_move(&page->lru, &clean_pages);
> > + }
> > +
> > + ret = shrink_page_list(&clean_pages, NULL, &sc, NULL, NULL);
> > + list_splice(&clean_pages, page_list);
> > + return ret;
> > +}
> > +
>
> It's different with my point.
> My intention is to free mapped clean pages as well as not-mapped's one.
>

Then just set may_unmap == 1?

struct scan_control sc = {
.gfp_mask = GFP_KERNEL,
.may_unmap = 1,
.priority = DEF_PRIORITY
};
> How about this?
>
> From 0f6986e943e55929b4d7b0220a1c24a6bae1a24d Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@kernel.org>
> Date: Fri, 7 Sep 2012 11:20:48 +0900
> Subject: [PATCH] mm: cma: Discard clean pages during contiguous allocation
> instead of migration
>
> This patch introudes MIGRATE_DISCARD mode in migration.

This line is now redundant.

> It drops *clean cache pages* instead of migration so that
> migration latency could be reduced by avoiding (memcpy + page remapping).
> It's useful for CMA because latency of migration is very important rather
> than eviction of background processes's workingset. In addition, it needs

processes working set

> less free pages for migration targets so it could avoid memory reclaiming
> to get free pages, which is another factor increase latency.
>
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> Cc: Michal Nazarewicz <mina86@mina86.com>
> Cc: Rik van Riel <riel@redhat.com>
> Signed-off-by: Mel Gorman <mgorman@suse.de>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> mm/internal.h | 2 ++
> mm/page_alloc.c | 2 ++
> mm/vmscan.c | 42 ++++++++++++++++++++++++++++++++++++------
> 3 files changed, 40 insertions(+), 6 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 3314f79..be09a7e 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -355,3 +355,5 @@ extern unsigned long vm_mmap_pgoff(struct file *, unsigned long,
> unsigned long, unsigned long);
>
> extern void set_pageblock_order(void);
> +unsigned long reclaim_clean_pages_from_list(struct zone *zone,
> + struct list_head *page_list);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ba3100a..bf35e59 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5668,6 +5668,8 @@ static int __alloc_contig_migrate_range(unsigned long start, unsigned long end)
> break;
> }
>
> + reclaim_clean_pages_from_list(&cc.migratepages, cc.zone);
> +

The signature is zone, list_head but you pass in list_head, zone. I
expect that generates fun compile warnings and crashes at runtime.

The reason that I did not pass in zone to reclaim_clean_pages_from_list()
in my version is because I did not want to force the list to all be from the
same zone. That will just happen to be true but shrink_page_list() really
does not care about the zone from the perspective of this new function. It's
used for a debugging check (disable it if !zone) and setting ZONE_CONGESTED
which will never be important as far as reclaim_clean_pages_from_list()
is concerned. It will never call pageout().

It's up to you if you really want to pass zone in but I would not bother
if I was you :)

> ret = migrate_pages(&cc.migratepages,
> __alloc_contig_migrate_alloc,
> 0, false, MIGRATE_SYNC);
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 8d01243..525355e 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -674,8 +674,10 @@ static enum page_references page_check_references(struct page *page,
> static unsigned long shrink_page_list(struct list_head *page_list,
> struct zone *zone,
> struct scan_control *sc,
> + enum ttu_flags ttu_flags,
> unsigned long *ret_nr_dirty,
> - unsigned long *ret_nr_writeback)
> + unsigned long *ret_nr_writeback,
> + bool force_reclaim)
> {
> LIST_HEAD(ret_pages);
> LIST_HEAD(free_pages);
> @@ -689,10 +691,10 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>
> mem_cgroup_uncharge_start();
> while (!list_empty(page_list)) {
> - enum page_references references;
> struct address_space *mapping;
> struct page *page;
> int may_enter_fs;
> + enum page_references references = PAGEREF_RECLAIM;
>
> cond_resched();
>
> @@ -758,7 +760,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> wait_on_page_writeback(page);
> }
>
> - references = page_check_references(page, sc);
> + if (!force_reclaim)
> + references = page_check_references(page, sc);
> +
> switch (references) {
> case PAGEREF_ACTIVATE:
> goto activate_locked;

Good point.

> @@ -788,7 +792,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> * processes. Try to unmap it here.
> */
> if (page_mapped(page) && mapping) {
> - switch (try_to_unmap(page, TTU_UNMAP)) {
> + switch (try_to_unmap(page, ttu_flags)) {
> case SWAP_FAIL:
> goto activate_locked;
> case SWAP_AGAIN:

Another good point.

> @@ -960,6 +964,32 @@ keep:
> return nr_reclaimed;
> }
>
> +unsigned long reclaim_clean_pages_from_list(struct zone *zone,
> + struct list_head *page_list)
> +{
> + struct scan_control sc = {
> + .gfp_mask = GFP_KERNEL,
> + .priority = DEF_PRIORITY,
> + .may_unmap = 1,
> + };

Yep.

> + unsigned long ret, dummy1, dummy2;
> + struct page *page, *next;
> + LIST_HEAD(clean_pages);
> +
> + list_for_each_entry_safe(page, next, page_list, lru) {
> + if (page_is_file_cache(page) && !PageDirty(page)) {
> + ClearPageActive(page);

Yep.

> + list_move(&page->lru, &clean_pages);
> + }
> + }
> +
> + ret = shrink_page_list(&clean_pages, zone, &sc,
> + TTU_UNMAP|TTU_IGNORE_ACCESS,
> + &dummy1, &dummy2, true);
> + list_splice(&clean_pages, page_list);
> + return ret;
> +}
> +
> /*
> * Attempt to remove the specified page from its LRU. Only take this page
> * if it is of the appropriate PageActive status. Pages which are being
> @@ -1278,8 +1308,8 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> if (nr_taken == 0)
> return 0;
>
> - nr_reclaimed = shrink_page_list(&page_list, zone, sc,
> - &nr_dirty, &nr_writeback);
> + nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
> + &nr_dirty, &nr_writeback, false);
>
> spin_lock_irq(&zone->lru_lock);
>

So other than the mix up of order parameters I think this should work.

--
Mel Gorman
SUSE Labs


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