From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Minchan Kim <minchan@kernel.org>, Mel Gorman <mgorman@suse.de>,
Michal Nazarewicz <mina86@mina86.com>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Christoph Lameter <cl@linux.com>, Rik van Riel <riel@redhat.com>,
David Rientjes <rientjes@google.com>
Subject: Re: [PATCH 4/6] mm, compaction: always skip compound pages by order in migrate scanner
Date: Tue, 16 Jun 2015 14:44:36 +0900 [thread overview]
Message-ID: <20150616054436.GD12641@js1304-P5Q-DELUXE> (raw)
In-Reply-To: <1433928754-966-5-git-send-email-vbabka@suse.cz>
On Wed, Jun 10, 2015 at 11:32:32AM +0200, Vlastimil Babka wrote:
> The compaction migrate scanner tries to skip compound pages by their order, to
> reduce number of iterations for pages it cannot isolate. The check is only done
> if PageLRU() is true, which means it applies to THP pages, but not e.g.
> hugetlbfs pages or any other non-LRU compound pages, which we have to iterate
> by base pages.
>
> This limitation comes from the assumption that it's only safe to read
> compound_order() when we have the zone's lru_lock and THP cannot be split under
> us. But the only danger (after filtering out order values that are not below
> MAX_ORDER, to prevent overflows) is that we skip too much or too little after
> reading a bogus compound_order() due to a rare race. This is the same reasoning
> as patch 99c0fd5e51c4 ("mm, compaction: skip buddy pages by their order in the
> migrate scanner") introduced for unsafely reading PageBuddy() order.
>
> After this patch, all pages are tested for PageCompound() and we skip them by
> compound_order(). The test is done after the test for balloon_page_movable()
> as we don't want to assume if balloon pages (or other pages with own isolation
> and migration implementation if a generic API gets implemented) are compound
> or not.
>
> When tested with stress-highalloc from mmtests on 4GB system with 1GB hugetlbfs
> pages, the vmstat compact_migrate_scanned count decreased by 15%.
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Michal Nazarewicz <mina86@mina86.com>
> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: David Rientjes <rientjes@google.com>
> ---
> mm/compaction.c | 36 +++++++++++++++++-------------------
> 1 file changed, 17 insertions(+), 19 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index d334bb3..e37d361 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -680,6 +680,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>
> /* Time to isolate some pages for migration */
> for (; low_pfn < end_pfn; low_pfn++) {
> + bool is_lru;
> +
> /*
> * Periodically drop the lock (if held) regardless of its
> * contention, to give chance to IRQs. Abort async compaction
> @@ -723,39 +725,35 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> * It's possible to migrate LRU pages and balloon pages
> * Skip any other type of page
> */
> - if (!PageLRU(page)) {
> + is_lru = PageLRU(page);
> + if (!is_lru) {
> if (unlikely(balloon_page_movable(page))) {
> if (balloon_page_isolate(page)) {
> /* Successfully isolated */
> goto isolate_success;
> }
> }
> - continue;
> }
>
> /*
> - * PageLRU is set. lru_lock normally excludes isolation
> - * splitting and collapsing (collapsing has already happened
> - * if PageLRU is set) but the lock is not necessarily taken
> - * here and it is wasteful to take it just to check transhuge.
> - * Check PageCompound without lock and skip the whole pageblock
> - * if it's a transhuge page, as calling compound_order()
> - * without preventing THP from splitting the page underneath us
> - * may return surprising results.
> - * If we happen to check a THP tail page, compound_order()
> - * returns 0. It should be rare enough to not bother with
> - * using compound_head() in that case.
> + * Regardless of being on LRU, compound pages such as THP and
> + * hugetlbfs are not to be compacted. We can potentially save
> + * a lot of iterations if we skip them at once. The check is
> + * racy, but we can consider only valid values and the only
> + * danger is skipping too much.
> */
> if (PageCompound(page)) {
> - int nr;
> - if (locked)
> - nr = 1 << compound_order(page);
> - else
> - nr = pageblock_nr_pages;
> - low_pfn += nr - 1;
> + unsigned int comp_order = compound_order(page);
> +
> + if (comp_order > 0 && comp_order < MAX_ORDER)
> + low_pfn += (1UL << comp_order) - 1;
> +
> continue;
> }
How about moving this PageCompound() check up to the PageLRU check?
Is there any relationship between balloon page and PageCompound()?
It will remove is_lru and code would be more understandable.
Otherwise,
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Thanks.
WARNING: multiple messages have this Message-ID (diff)
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Minchan Kim <minchan@kernel.org>, Mel Gorman <mgorman@suse.de>,
Michal Nazarewicz <mina86@mina86.com>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Christoph Lameter <cl@linux.com>, Rik van Riel <riel@redhat.com>,
David Rientjes <rientjes@google.com>
Subject: Re: [PATCH 4/6] mm, compaction: always skip compound pages by order in migrate scanner
Date: Tue, 16 Jun 2015 14:44:36 +0900 [thread overview]
Message-ID: <20150616054436.GD12641@js1304-P5Q-DELUXE> (raw)
In-Reply-To: <1433928754-966-5-git-send-email-vbabka@suse.cz>
On Wed, Jun 10, 2015 at 11:32:32AM +0200, Vlastimil Babka wrote:
> The compaction migrate scanner tries to skip compound pages by their order, to
> reduce number of iterations for pages it cannot isolate. The check is only done
> if PageLRU() is true, which means it applies to THP pages, but not e.g.
> hugetlbfs pages or any other non-LRU compound pages, which we have to iterate
> by base pages.
>
> This limitation comes from the assumption that it's only safe to read
> compound_order() when we have the zone's lru_lock and THP cannot be split under
> us. But the only danger (after filtering out order values that are not below
> MAX_ORDER, to prevent overflows) is that we skip too much or too little after
> reading a bogus compound_order() due to a rare race. This is the same reasoning
> as patch 99c0fd5e51c4 ("mm, compaction: skip buddy pages by their order in the
> migrate scanner") introduced for unsafely reading PageBuddy() order.
>
> After this patch, all pages are tested for PageCompound() and we skip them by
> compound_order(). The test is done after the test for balloon_page_movable()
> as we don't want to assume if balloon pages (or other pages with own isolation
> and migration implementation if a generic API gets implemented) are compound
> or not.
>
> When tested with stress-highalloc from mmtests on 4GB system with 1GB hugetlbfs
> pages, the vmstat compact_migrate_scanned count decreased by 15%.
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Michal Nazarewicz <mina86@mina86.com>
> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: David Rientjes <rientjes@google.com>
> ---
> mm/compaction.c | 36 +++++++++++++++++-------------------
> 1 file changed, 17 insertions(+), 19 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index d334bb3..e37d361 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -680,6 +680,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>
> /* Time to isolate some pages for migration */
> for (; low_pfn < end_pfn; low_pfn++) {
> + bool is_lru;
> +
> /*
> * Periodically drop the lock (if held) regardless of its
> * contention, to give chance to IRQs. Abort async compaction
> @@ -723,39 +725,35 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> * It's possible to migrate LRU pages and balloon pages
> * Skip any other type of page
> */
> - if (!PageLRU(page)) {
> + is_lru = PageLRU(page);
> + if (!is_lru) {
> if (unlikely(balloon_page_movable(page))) {
> if (balloon_page_isolate(page)) {
> /* Successfully isolated */
> goto isolate_success;
> }
> }
> - continue;
> }
>
> /*
> - * PageLRU is set. lru_lock normally excludes isolation
> - * splitting and collapsing (collapsing has already happened
> - * if PageLRU is set) but the lock is not necessarily taken
> - * here and it is wasteful to take it just to check transhuge.
> - * Check PageCompound without lock and skip the whole pageblock
> - * if it's a transhuge page, as calling compound_order()
> - * without preventing THP from splitting the page underneath us
> - * may return surprising results.
> - * If we happen to check a THP tail page, compound_order()
> - * returns 0. It should be rare enough to not bother with
> - * using compound_head() in that case.
> + * Regardless of being on LRU, compound pages such as THP and
> + * hugetlbfs are not to be compacted. We can potentially save
> + * a lot of iterations if we skip them at once. The check is
> + * racy, but we can consider only valid values and the only
> + * danger is skipping too much.
> */
> if (PageCompound(page)) {
> - int nr;
> - if (locked)
> - nr = 1 << compound_order(page);
> - else
> - nr = pageblock_nr_pages;
> - low_pfn += nr - 1;
> + unsigned int comp_order = compound_order(page);
> +
> + if (comp_order > 0 && comp_order < MAX_ORDER)
> + low_pfn += (1UL << comp_order) - 1;
> +
> continue;
> }
How about moving this PageCompound() check up to the PageLRU check?
Is there any relationship between balloon page and PageCompound()?
It will remove is_lru and code would be more understandable.
Otherwise,
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Thanks.
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next prev parent reply other threads:[~2015-06-16 5:42 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-10 9:32 [PATCH 0/6] Assorted compaction cleanups and optimizations Vlastimil Babka
2015-06-10 9:32 ` Vlastimil Babka
2015-06-10 9:32 ` [PATCH 1/6] mm, compaction: more robust check for scanners meeting Vlastimil Babka
2015-06-10 9:32 ` Vlastimil Babka
2015-06-10 18:02 ` Rik van Riel
2015-06-10 18:02 ` Rik van Riel
2015-06-12 9:55 ` Michal Nazarewicz
2015-06-12 9:55 ` Michal Nazarewicz
2015-06-16 5:37 ` Joonsoo Kim
2015-06-16 5:37 ` Joonsoo Kim
2015-06-19 13:41 ` Mel Gorman
2015-06-19 13:41 ` Mel Gorman
2015-06-10 9:32 ` [PATCH 2/6] mm, compaction: simplify handling restart position in free pages scanner Vlastimil Babka
2015-06-10 9:32 ` Vlastimil Babka
2015-06-16 5:38 ` Joonsoo Kim
2015-06-16 5:38 ` Joonsoo Kim
2015-06-19 13:48 ` Mel Gorman
2015-06-19 13:48 ` Mel Gorman
2015-06-10 9:32 ` [PATCH 3/6] mm, compaction: encapsulate resetting cached scanner positions Vlastimil Babka
2015-06-10 9:32 ` Vlastimil Babka
2015-06-12 10:07 ` Michal Nazarewicz
2015-06-12 10:07 ` Michal Nazarewicz
2015-06-16 5:41 ` Joonsoo Kim
2015-06-16 5:41 ` Joonsoo Kim
2015-06-16 12:13 ` Vlastimil Babka
2015-06-16 12:13 ` Vlastimil Babka
2015-06-10 9:32 ` [PATCH 4/6] mm, compaction: always skip compound pages by order in migrate scanner Vlastimil Babka
2015-06-10 9:32 ` Vlastimil Babka
2015-06-12 10:11 ` Michal Nazarewicz
2015-06-12 10:11 ` Michal Nazarewicz
2015-06-16 5:44 ` Joonsoo Kim [this message]
2015-06-16 5:44 ` Joonsoo Kim
2015-06-16 12:16 ` Vlastimil Babka
2015-06-16 12:16 ` Vlastimil Babka
2015-06-19 13:58 ` Mel Gorman
2015-06-19 13:58 ` Mel Gorman
2015-06-10 9:32 ` [PATCH 5/6] mm, compaction: skip compound pages by order in free scanner Vlastimil Babka
2015-06-10 9:32 ` Vlastimil Babka
2015-06-12 10:18 ` Michal Nazarewicz
2015-06-12 10:18 ` Michal Nazarewicz
2015-06-16 5:45 ` Joonsoo Kim
2015-06-16 5:45 ` Joonsoo Kim
2015-06-10 9:32 ` [PATCH 6/6] mm, compaction: decouple updating pageblock_skip and cached pfn Vlastimil Babka
2015-06-10 9:32 ` Vlastimil Babka
2015-06-16 6:10 ` Joonsoo Kim
2015-06-16 6:10 ` Joonsoo Kim
2015-06-16 12:33 ` Vlastimil Babka
2015-06-16 12:33 ` Vlastimil Babka
2015-06-16 13:03 ` Joonsoo Kim
2015-06-16 13:03 ` Joonsoo Kim
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