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From: Gao Xiang <xiang@kernel.org>
To: linux-erofs@lists.ozlabs.org
Cc: Matthew Wilcox <willy@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>, Gao Xiang <xiang@kernel.org>
Subject: [PATCH 1/2] erofs: better comment z_erofs_readahead()
Date: Tue,  6 Jul 2021 02:32:52 +0800	[thread overview]
Message-ID: <20210705183253.14833-1-xiang@kernel.org> (raw)

Add some words about the traversal order and its pagepool usage.

Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Gao Xiang <xiang@kernel.org>
---
 fs/erofs/zdata.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index cb4d0889eca9..054b9839e9db 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1424,6 +1424,16 @@ static void z_erofs_readahead(struct readahead_control *rac)
 	f.readahead = true;
 	f.headoffset = readahead_pos(rac);
 
+	/*
+	 * All pages are locked in the forward order in advance, so directly
+	 * traverse pages in the reverse order since:
+	 *  1) more effective to get each extent start offset, calculate partial
+	 *     decompressed length w/o knowing the full extent length (which is
+	 *     more metadata costly). If traversing in the normal order, it's
+	 *     mandatory to get full extent length one-by-one.
+	 *  2) submission chain can be then in the forward order since
+	 *     pclusters are all inserted at head.
+	 */
 	while ((page = readahead_page(rac))) {
 		prefetchw(&page->flags);
 
@@ -1460,7 +1470,7 @@ static void z_erofs_readahead(struct readahead_control *rac)
 	if (f.map.mpage)
 		put_page(f.map.mpage);
 
-	/* clean up the remaining free pages */
+	/* drain the on-stack pagepool with unused non-LRU temporary pages */
 	put_pages_list(&pagepool);
 }
 
-- 
2.20.1


WARNING: multiple messages have this Message-ID (diff)
From: Gao Xiang <xiang@kernel.org>
To: linux-erofs@lists.ozlabs.org
Cc: Gao Xiang <xiang@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
	Matthew Wilcox <willy@infradead.org>
Subject: [PATCH 1/2] erofs: better comment z_erofs_readahead()
Date: Tue,  6 Jul 2021 02:32:52 +0800	[thread overview]
Message-ID: <20210705183253.14833-1-xiang@kernel.org> (raw)

Add some words about the traversal order and its pagepool usage.

Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Gao Xiang <xiang@kernel.org>
---
 fs/erofs/zdata.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index cb4d0889eca9..054b9839e9db 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1424,6 +1424,16 @@ static void z_erofs_readahead(struct readahead_control *rac)
 	f.readahead = true;
 	f.headoffset = readahead_pos(rac);
 
+	/*
+	 * All pages are locked in the forward order in advance, so directly
+	 * traverse pages in the reverse order since:
+	 *  1) more effective to get each extent start offset, calculate partial
+	 *     decompressed length w/o knowing the full extent length (which is
+	 *     more metadata costly). If traversing in the normal order, it's
+	 *     mandatory to get full extent length one-by-one.
+	 *  2) submission chain can be then in the forward order since
+	 *     pclusters are all inserted at head.
+	 */
 	while ((page = readahead_page(rac))) {
 		prefetchw(&page->flags);
 
@@ -1460,7 +1470,7 @@ static void z_erofs_readahead(struct readahead_control *rac)
 	if (f.map.mpage)
 		put_page(f.map.mpage);
 
-	/* clean up the remaining free pages */
+	/* drain the on-stack pagepool with unused non-LRU temporary pages */
 	put_pages_list(&pagepool);
 }
 
-- 
2.20.1


             reply	other threads:[~2021-07-05 18:33 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-05 18:32 Gao Xiang [this message]
2021-07-05 18:32 ` [PATCH 1/2] erofs: better comment z_erofs_readahead() Gao Xiang
2021-07-05 18:32 ` [RFC PATCH 2/2] erofs: directly traverse pages in z_erofs_readahead() Gao Xiang
2021-07-05 18:32   ` Gao Xiang
2021-07-05 20:15   ` Matthew Wilcox
2021-07-05 22:48     ` Gao Xiang

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