linux-kernel - [PATCH 0/2] mm/ksm: optimize unstable_tree_search

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Message-Id: <20240508-b4-ksm-unstable-insert-v1-0-631cdbc2b77f@linux.dev>
Date: Wed, 08 May 2024 19:35:40 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>, 
 David Hildenbrand <david@...hat.com>, 
 Andrea Arcangeli <aarcange@...hat.com>, Stefan Roesch <shr@...kernel.io>, 
 Hugh Dickins <hughd@...gle.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
 zhouchengming@...edance.com, Chengming Zhou <chengming.zhou@...ux.dev>
Subject: [PATCH 0/2] mm/ksm: optimize unstable_tree_search_insert()

We use unstable_tree_search_insert() to find matched page or insert our
rmap_item into the unstable tree if no matched found.

Now it may return NULL too early in which cases we can do better:

1. get_mergeable_page() return NULL: which means tree_rmap_item is stale.
2. tree_page is migrated to another node and !ksm_merge_across_nodes.

In both cases, we can just remove the staled or migrated one out of the
unstable tree, so our rmap_item can be inserted successfully. The code
flow becomes clearer and may increase the merge possibility too.

Thanks for review and comments!

Signed-off-by: Chengming Zhou <chengming.zhou@...ux.dev>
---
Chengming Zhou (2):
      mm/ksm: re-search unstable tree when tree_rmap_item is stale
      mm/ksm: flush out migrated rmap_item to insert our rmap_item

 mm/ksm.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)
---
base-commit: fb0f40125feec3de7ef4524600ac83946207117e
change-id: 20240508-b4-ksm-unstable-insert-0329446317e1

Best regards,
-- 
Chengming Zhou <chengming.zhou@...ux.dev>