linux-kernel - [PATCH RFC md-6.16 v3 13/19] md/md-llbitmap: implement APIs for page level dirty bits synchronization

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Message-Id: <20250512011927.2809400-14-yukuai1@huaweicloud.com>
Date: Mon, 12 May 2025 09:19:21 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: hch@....de,
	xni@...hat.com,
	colyli@...nel.org,
	agk@...hat.com,
	snitzer@...nel.org,
	mpatocka@...hat.com,
	song@...nel.org,
	yukuai3@...wei.com
Cc: linux-kernel@...r.kernel.org,
	dm-devel@...ts.linux.dev,
	linux-raid@...r.kernel.org,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: [PATCH RFC md-6.16 v3 13/19] md/md-llbitmap: implement APIs for page level dirty bits synchronization

From: Yu Kuai <yukuai3@...wei.com>

IO fast path will set bits to dirty, and those dirty bits will be cleared
by daemon after IO is done. llbitmap_barrier is used to synchronize between
IO path and daemon;

IO path:
 1) try to grab a reference, if succeed, set expire time after 5s and
 return;
 2) if failed to grab a reference, wait for daemon to finish clearing dirty
 bits;

Daemon(Daemon will be waken up every daemon_sleep seconds):
For each page:
 1) check if page expired, if not skip this page; for expired page:
 2) suspend the page and wait for inflight write IO to be done;
 3) change dirty page to clean;
 4) resume the page;

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 drivers/md/md-llbitmap.c | 46 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/drivers/md/md-llbitmap.c b/drivers/md/md-llbitmap.c
index 315a4eb7627c..994ca0be3d17 100644
--- a/drivers/md/md-llbitmap.c
+++ b/drivers/md/md-llbitmap.c
@@ -435,6 +435,14 @@ static void llbitmap_write_page(struct llbitmap *llbitmap, int idx)
 	}
 }
 
+static void active_release(struct percpu_ref *ref)
+{
+	struct llbitmap_barrier *barrier =
+		container_of(ref, struct llbitmap_barrier, active);
+
+	wake_up(&barrier->wait);
+}
+
 static int llbitmap_cache_pages(struct llbitmap *llbitmap)
 {
 	int nr_pages = (llbitmap->chunks + BITMAP_SB_SIZE + PAGE_SIZE - 1) / PAGE_SIZE;
@@ -562,3 +570,41 @@ static enum llbitmap_state llbitmap_state_machine(struct llbitmap *llbitmap,
 
 	return state;
 }
+
+static void llbitmap_raise_barrier(struct llbitmap *llbitmap, int page_idx)
+{
+	struct llbitmap_barrier *barrier = &llbitmap->barrier[page_idx];
+
+retry:
+	if (likely(percpu_ref_tryget_live(&barrier->active))) {
+		WRITE_ONCE(barrier->expire, jiffies + BARRIER_IDLE * HZ);
+		return;
+	}
+
+	wait_event(barrier->wait, !percpu_ref_is_dying(&barrier->active));
+	goto retry;
+}
+
+static void llbitmap_release_barrier(struct llbitmap *llbitmap, int page_idx)
+{
+	struct llbitmap_barrier *barrier = &llbitmap->barrier[page_idx];
+
+	percpu_ref_put(&barrier->active);
+}
+
+static void llbitmap_suspend(struct llbitmap *llbitmap, int page_idx)
+{
+	struct llbitmap_barrier *barrier = &llbitmap->barrier[page_idx];
+
+	percpu_ref_kill(&barrier->active);
+	wait_event(barrier->wait, percpu_ref_is_zero(&barrier->active));
+}
+
+static void llbitmap_resume(struct llbitmap *llbitmap, int page_idx)
+{
+	struct llbitmap_barrier *barrier = &llbitmap->barrier[page_idx];
+
+	barrier->expire = LONG_MAX;
+	percpu_ref_resurrect(&barrier->active);
+	wake_up(&barrier->wait);
+}
-- 
2.39.2