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  1. 29 Jul, 2018 30 commits
  3. 28 Jul, 2018 6 commits
  5. 27 Jul, 2018 4 commits
    • Gao Xiang's avatar
      staging: erofs: add a TODO and update MAINTAINERS for staging · 27cce7bc
      Gao Xiang authored 
      This patch adds a TODO to list the things to be done, and
the relevant info to MAINTAINERS so we can take all the blame :)
Signed-off-by: default avatarGao Xiang <gaoxiang25@huawei.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      27cce7bc
    • Gao Xiang's avatar
      staging: erofs: introduce cached decompression · 105d4ad8
      Gao Xiang authored 
      This patch adds an optional choice which can be
enabled by users in order to cache both incomplete
ends of compressed clusters as a complement to
the in-place decompression in order to boost random
read, but it costs more memory than the in-place
decompression only.
Signed-off-by: default avatarGao Xiang <gaoxiang25@huawei.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      105d4ad8
    • Gao Xiang's avatar
      staging: erofs: introduce VLE decompression support · 3883a79a
      Gao Xiang authored 
      This patch introduces the basic in-place VLE decompression
implementation for the erofs file system.

Compared with fixed-sized input compression, it implements
what we call 'the variable-length extent compression' which
specifies the same output size for each compression block
to make the full use of IO bandwidth (which means almost
all data from block device can be directly used for decomp-
ression), improve the real (rather than just via data caching,
which costs more memory) random read and keep the relatively
lower compression ratios (it saves more storage space than
fixed-sized input compression which is also configured with
the same input block size), as illustrated below:

        |---  variable-length extent ---|------ VLE ------|---  VLE ---|
         /> clusterofs                  /> clusterofs     /> clusterofs /> clusterofs
   ++---|-------++-----------++---------|-++-----------++-|---------++-|
...||   |       ||           ||         | ||           || |         || | ... original data
   ++---|-------++-----------++---------|-++-----------++-|---------++-|
   ++->cluster<-++->cluster<-++->cluster<-++->cluster<-++->cluster<-++
        size         size         size         size         size
         \                             /                 /            /
          \                      /              /            /
           \               /            /            /
            ++-----------++-----------++-----------++
        ... ||           ||           ||           || ... compressed clusters
            ++-----------++-----------++-----------++
            ++->cluster<-++->cluster<-++->cluster<-++
                 size         size         size

The main point of 'in-place' refers to the decompression mode:
Instead of allocating independent compressed pages and data
structures, it reuses the allocated file cache pages at most
to store its compressed data and the corresponding pagevec in
a time-sharing approach by default, which will be useful for
low memory scenario.

In the end, unlike the other filesystems with (de)compression
support using a relatively large compression block size, which
reads and decompresses >= 128KB at once, and gains a more
good-looking random read (In fact it collects small random reads
into large sequential reads and caches all decompressed data
in memory, but it is unacceptable especially for embedded devices
with limited memory, and it is not the real random read), we
select a universal small-sized 4KB compressed cluster, which is
the smallest page size for most architectures, and all compressed
clusters can be read and decompressed independently, which ensures
random read number for all use cases.
Signed-off-by: default avatarGao Xiang <gaoxiang25@huawei.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      3883a79a
    • Gao Xiang's avatar
      staging: erofs: introduce workstation for decompression · e7e9a307
      Gao Xiang authored 
      This patch introduces another concept used by the unzip
subsystem called 'workstation'. It can be seen as a sparse
array that stores pointers pointed to data structures
related to the corresponding physical blocks.

All lookup cases are protected by RCU read lock. Besides,
reference count and spin_lock are also introduced to
manage its lifetime and serialize all update operations.

'workstation' is currently implemented on the in-kernel
radix tree approach for backward compatibility.
With the evolution of linux kernel, it could be migrated
into XArray implementation in the future.
Signed-off-by: default avatarGao Xiang <gaoxiang25@huawei.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      e7e9a307
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