On 02/02/2018 12:00 PM, Laurent Dufour wrote:
On 02/02/2018 15:40, Laurent Dufour wrote:
On 01/02/2018 00:04, daniel.m.jordan@xxxxxxxxxx wrote:
A common case in release_pages is for the 'pages' list to be in roughly
the same order as they are in their LRU. With LRU batch locking, when a
sentinel page is removed, an adjacent non-sentinel page must be promoted
to a sentinel page to follow the locking scheme. So we can get behavior
where nearly every page in the 'pages' array is treated as a sentinel
page, hurting the scalability of this approach.
To address this, split up release_pages into non-sentinel and sentinel
passes so that the non-sentinel pages can be locked with an LRU batch
lock before the sentinel pages are removed.
For the prototype, just use a bitmap and a temporary outer loop to
implement this.
Performance numbers from a single microbenchmark at this point in the
series are included in the next patch.
Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
---
mm/swap.c | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/mm/swap.c b/mm/swap.c
index fae766e035a4..a302224293ad 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -731,6 +731,7 @@ void lru_add_drain_all(void)
put_online_cpus();
}
+#define LRU_BITMAP_SIZE 512
/**
* release_pages - batched put_page()
* @pages: array of pages to release
@@ -742,16 +743,32 @@ void lru_add_drain_all(void)
*/
void release_pages(struct page **pages, int nr)
{
- int i;
+ int h, i;
LIST_HEAD(pages_to_free);
struct pglist_data *locked_pgdat = NULL;
spinlock_t *locked_lru_batch = NULL;
struct lruvec *lruvec;
unsigned long uninitialized_var(flags);
+ DECLARE_BITMAP(lru_bitmap, LRU_BITMAP_SIZE);
+
+ VM_BUG_ON(nr > LRU_BITMAP_SIZE);
While running your series rebased on v4.15-mmotm-2018-01-31-16-51, I'm
hitting this VM_BUG sometimes on a ppc64 system where page size is set to 64K.
I can't see any link between nr and LRU_BITMAP_SIZE, caller may pass a
larger list of pages which is not relative to the LRU list.
You're correct, I used the hard-coded size to quickly prototype, just to
see how this approach performs. That's unfortunate that it bit you.
> To move forward seeing the benefit of this series with the SPF one, I
declared the bit map based on nr. This is still not a valid option but this
at least allows to process all the passed pages.
Yes, the bitmap's not for the final version.
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