Re: [PATCH v3] memory_hotplug: Free pages as higher order

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On 2018-09-27 12:41, Juergen Gross wrote:
On 27/09/18 08:58, Arun KS wrote:
When free pages are done with higher order, time spend on
coalescing pages by buddy allocator can be reduced. With
section size of 256MB, hot add latency of a single section
shows improvement from 50-60 ms to less than 1 ms, hence
improving the hot add latency by 60%.

Modify external providers of online callback to align with
the change.

Signed-off-by: Arun KS <arunks@xxxxxxxxxxxxxx>
---
Changes since v2:
reuse code from __free_pages_boot_core()

Changes since v1:
- Removed prefetch()

Changes since RFC:
- Rebase.
- As suggested by Michal Hocko remove pages_per_block.
- Modifed external providers of online_page_callback.

v2: https://lore.kernel.org/patchwork/patch/991363/
v1: https://lore.kernel.org/patchwork/patch/989445/
RFC: https://lore.kernel.org/patchwork/patch/984754/

---
 drivers/hv/hv_balloon.c        |  6 ++++--
 drivers/xen/balloon.c          | 18 ++++++++++++++---
 include/linux/memory_hotplug.h |  2 +-
 mm/internal.h                  |  1 +
mm/memory_hotplug.c | 44 ++++++++++++++++++++++++++++++------------
 mm/page_alloc.c                |  2 +-
 6 files changed, 54 insertions(+), 19 deletions(-)


...

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index e12bb25..010cf4d 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -390,8 +390,8 @@ static enum bp_state reserve_additional_memory(void)

 	/*
 	 * add_memory_resource() will call online_pages() which in its turn
-	 * will call xen_online_page() callback causing deadlock if we don't
-	 * release balloon_mutex here. Unlocking here is safe because the
+	 * will call xen_bring_pgs_online() callback causing deadlock if we
+ * don't release balloon_mutex here. Unlocking here is safe because the
 	 * callers drop the mutex before trying again.
 	 */
 	mutex_unlock(&balloon_mutex);
@@ -422,6 +422,18 @@ static void xen_online_page(struct page *page)
 	mutex_unlock(&balloon_mutex);
 }

+static int xen_bring_pgs_online(struct page *pg, unsigned int order)
+{
+	unsigned long i, size = (1 << order);
+	unsigned long start_pfn = page_to_pfn(pg);
+
+ pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, start_pfn);
+	for (i = 0; i < size; i++)
+		xen_online_page(pfn_to_page(start_pfn + i));


Hi,

xen_online_page() isn't very complex and this is the only user.

Why don't you move its body in here and drop the extra function?
And now you can execute the loop with balloon_mutex held instead of
taking and releasing it in each iteration of the loop.
Point taken. Will incorporate them.

Regards,
Arun


Juergen
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