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From: Gao Xiang <xiang@kernel.org>
To: linux-erofs@lists.ozlabs.org
Cc: Gao Xiang <xiang@kernel.org>
Subject: [PATCH 2/2] erofs-utils: README: big pcluster feature update
Date: Sat, 22 May 2021 13:50:57 +0800	[thread overview]
Message-ID: <20210522055057.25004-2-xiang@kernel.org> (raw)
In-Reply-To: <20210522055057.25004-1-xiang@kernel.org>

Add some description for end users to know its usage.

Signed-off-by: Gao Xiang <xiang@kernel.org>
---
 README | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/README b/README
index bcf30e11aa52..567192c8c497 100644
--- a/README
+++ b/README
@@ -74,6 +74,24 @@ In addition, you could specify a higher compression level to get a
 (slightly) better compression ratio than the default level, e.g.
  $ mkfs.erofs -zlz4hc,12 foo.erofs.img foo/
 
+How to generate EROFS big pcluster images (Linux 5.13+)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In order to get much better compression ratios (thus better sequential
+read performance for common storage devices), big pluster feature has
+been introduced since linux-5.13, which is not forward-compatible with
+old kernels.
+
+In details, -C is used to specify the maximum size of each big pcluster
+in bytes, e.g.
+ $ mkfs.erofs -zlz4hc -C65536 foo.erofs.img foo/
+
+So in that case, pcluster size can be 64KiB at most.
+
+Note that large big pcluster size can cause bad random performance, so
+please evaluate carefully in advance. Or make your own per-(sub)file
+compression strategies according to file access patterns if needed.
+
 How to generate legacy EROFS images (Linux 4.19+)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-- 
2.20.1


      reply	other threads:[~2021-05-22  5:51 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-22  5:50 [PATCH 1/2] erofs-utils: README: trivial updates Gao Xiang
2021-05-22  5:50 ` Gao Xiang [this message]

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