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Date: Fri, 7 Sep 2012 16:31:17 +0900
From: Kyungmin Park <kmpark@...radead.org>
To: Minchan Kim <minchan@...nel.org>
Cc: Mel Gorman <mgorman@...e.de>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Michal Nazarewicz <mina86@...a86.com>,
Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/2] mm: support MIGRATE_DISCARD
On 9/7/12, Kyungmin Park <kmpark@...radead.org> wrote:
> Hi Minchan,
>
> I tested Mel patch again with ClearPageActive(page). but after some
> testing, it's stall and can't return from
> reclaim_clean_pages_from_list(&cc.migratepages).
>
> Maybe it's related with unmap feature from yours?
> stall is not happened from your codes until now.
>
> I'll test it more and report any issue if happened.
Updated. it's hang also. there are other issues.
>
> Thank you,
> Kyungmin Park
>
> On 9/7/12, Minchan Kim <minchan@...nel.org> wrote:
>> On Thu, Sep 06, 2012 at 10:03:25AM +0100, Mel Gorman wrote:
>>> On Thu, Sep 06, 2012 at 09:29:35AM +0100, Mel Gorman wrote:
>>> > On Thu, Sep 06, 2012 at 02:31:12PM +0900, Minchan Kim wrote:
>>> > > Hi Mel,
>>> > >
>>> > > On Wed, Sep 05, 2012 at 11:56:11AM +0100, Mel Gorman wrote:
>>> > > > On Wed, Sep 05, 2012 at 05:11:13PM +0900, Minchan Kim wrote:
>>> > > > > This patch introudes MIGRATE_DISCARD mode in migration.
>>> > > > > 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
>>> > > > > less free pages for migration targets so it could avoid memory
>>> > > > > reclaiming
>>> > > > > to get free pages, which is another factor increase latency.
>>> > > > >
>>> > > >
>>> > > > Bah, this was released while I was reviewing the older version. I
>>> > > > did
>>> > > > not read this one as closely but I see the enum problems have gone
>>> > > > away
>>> > > > at least. I'd still prefer if CMA had an additional helper to
>>> > > > discard
>>> > > > some pages with shrink_page_list() and migrate the remaining pages
>>> > > > with
>>> > > > migrate_pages(). That would remove the need to add a
>>> > > > MIGRATE_DISCARD
>>> > > > migrate mode at all.
>>> > >
>>> > > I am not convinced with your point. What's the benefit on separating
>>> > > reclaim and migration? For just removing MIGRATE_DISCARD mode?
>>> >
>>> > Maintainability. There are reclaim functions and there are migration
>>> > functions. Your patch takes migrate_pages() and makes it partially a
>>> > reclaim function mixing up the responsibilities of migrate.c and
>>> > vmscan.c.
>>> >
>>> > > I don't think it's not bad because my implementation is very
>>> > > simple(maybe
>>> > > it's much simpler than separating reclaim and migration) and
>>> > > could be used by others like memory-hotplug in future.
>>> >
>>> > They could also have used the helper function from CMA that takes a
>>> > list
>>> > of pages, reclaims some and migrates other.
>>> >
>>>
>>> I also do not accept that your approach is inherently simpler than what
>>> I
>>> proposed to you. This is not tested at all but it should be functionally
>>> similar to both your patches except that it keeps the responsibility for
>>> reclaim in vmscan.c
>>>
>>> Your diffstats are
>>>
>>> 8 files changed, 39 insertions(+), 36 deletions(-)
>>> 3 files changed, 46 insertions(+), 4 deletions(-)
>>>
>>> Mine is
>>>
>>> 3 files changed, 32 insertions(+), 5 deletions(-)
>>>
>>> Fewer files changed and fewer lines inserted.
>>>
>>> ---8<---
>>> mm: cma: Discard clean pages during contiguous allocation instead of
>>> migration
>>>
>>> This patch drops clean cache pages instead of migration during
>>> alloc_contig_range() to minimise allocation latency by reducing the
>>> amount
>>> of migration is necessary. It's useful for CMA because latency of
>>> migration
>>> is more important than evicting the background processes working set.
>>>
>>> Prototype-not-signed-off-but-feel-free-to-pick-up-and-test
>>> ---
>>> mm/internal.h | 1 +
>>> mm/page_alloc.c | 2 ++
>>> mm/vmscan.c | 34 +++++++++++++++++++++++++++++-----
>>> 3 files changed, 32 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/mm/internal.h b/mm/internal.h
>>> index b8c91b3..6d4bdf9 100644
>>> --- a/mm/internal.h
>>> +++ b/mm/internal.h
>>> @@ -356,3 +356,4 @@ 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 list_head
>>> *page_list);
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index c66fb87..977bdb2 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -5670,6 +5670,8 @@ static int __alloc_contig_migrate_range(unsigned
>>> long start, unsigned long end)
>>> break;
>>> }
>>>
>>> + reclaim_clean_pages_from_list(&cc.migratepages);
>>> +
>>> 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..ccf7bc2 100644
>>> --- a/mm/vmscan.c
>>> +++ b/mm/vmscan.c
>>> @@ -703,7 +703,7 @@ static unsigned long shrink_page_list(struct
>>> list_head
>>> *page_list,
>>> goto keep;
>>>
>>> VM_BUG_ON(PageActive(page));
>>> - VM_BUG_ON(page_zone(page) != zone);
>>> + VM_BUG_ON(zone && page_zone(page) != zone);
>>>
>>> sc->nr_scanned++;
>>>
>>> @@ -817,7 +817,9 @@ static unsigned long shrink_page_list(struct
>>> list_head
>>> *page_list,
>>> * except we already have the page isolated
>>> * and know it's dirty
>>> */
>>> - inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
>>> + if (zone)
>>> + inc_zone_page_state(page,
>>> + NR_VMSCAN_IMMEDIATE);
>>> SetPageReclaim(page);
>>>
>>> goto keep_locked;
>>> @@ -947,7 +949,7 @@ keep:
>>> * back off and wait for congestion to clear because further reclaim
>>> * will encounter the same problem
>>> */
>>> - if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
>>> + if (zone && nr_dirty && nr_dirty == nr_congested &&
>>> global_reclaim(sc))
>>> zone_set_flag(zone, ZONE_CONGESTED);
>>>
>>> free_hot_cold_page_list(&free_pages, 1);
>>> @@ -955,11 +957,33 @@ keep:
>>> list_splice(&ret_pages, page_list);
>>> count_vm_events(PGACTIVATE, pgactivate);
>>> mem_cgroup_uncharge_end();
>>> - *ret_nr_dirty += nr_dirty;
>>> - *ret_nr_writeback += nr_writeback;
>>> + if (ret_nr_dirty)
>>> + *ret_nr_dirty += nr_dirty;
>>> + if (ret_nr_writeback)
>>> + *ret_nr_writeback += nr_writeback;
>>> return nr_reclaimed;
>>> }
>>>
>>> +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.
>>
>> How about this?
>>
>> From 0f6986e943e55929b4d7b0220a1c24a6bae1a24d Mon Sep 17 00:00:00 2001
>> From: Minchan Kim <minchan@...nel.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.
>> 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
>> 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@...sung.com>
>> Cc: Michal Nazarewicz <mina86@...a86.com>
>> Cc: Rik van Riel <riel@...hat.com>
>> Signed-off-by: Mel Gorman <mgorman@...e.de>
>> Signed-off-by: Minchan Kim <minchan@...nel.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);
>> +
>> 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;
>> @@ -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:
>> @@ -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,
>> + };
>> + 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);
>> + 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);
>>
>> --
>> 1.7.9.5
>>
>> --
>> Kind regards,
>> Minchan Kim
>>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@...ck.org. For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
>>
>
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