From f268eedddf3595e85f8883dc50aed29654785696 Mon Sep 17 00:00:00 2001 From: Phillip Lougher Date: Sat, 11 Jun 2022 04:21:32 +0100 Subject: squashfs: extend "page actor" to handle missing pages Patch series "Squashfs: handle missing pages decompressing into page cache". This patchset enables Squashfs to handle missing pages when directly decompressing datablocks into the page cache. Previously if the full set of pages needed was not available, Squashfs would have to fall back to using an intermediate buffer (the older method), which is slower, involving a memcopy, and it introduces contention on a shared buffer. The first patch extends the "page actor" code to handle missing pages. The second patch updates Squashfs_readpage_block() to use the new functionality, and removes the code that falls back to using an intermediate buffer. This patchset is independent of the readahead work, and it is standalone. It can be merged on its own. But the readahead patch for efficiency also needs this patch-set. This patch (of 2): This patch extends the "page actor" code to handle missing pages. Previously if the full set of pages needed to decompress a Squashfs datablock was unavailable, this would cause decompression to fail on the missing pages. In this case direct decompression into the page cache could not be achieved and the code would fall back to using the older intermediate buffer method. With this patch, direct decompression into the page cache can be achieved with missing pages. For "multi-shot" decompressors (zlib, xz, zstd), the page actor will allocate a temporary buffer which is passed to the decompressor, and then freed by the page actor. For "single shot" decompressors (lz4, lzo) which decompress into a contiguous "bounce buffer", and which is then copied into the page cache, it would be pointless to allocate a temporary buffer, memcpy into it, and then free it. For these decompressors -ENOMEM is returned, which signifies that the memcpy for that page should be skipped. This also happens if the data block is uncompressed. Link: https://lkml.kernel.org/r/20220611032133.5743-1-phillip@squashfs.org.uk Link: https://lkml.kernel.org/r/20220611032133.5743-2-phillip@squashfs.org.uk Signed-off-by: Phillip Lougher Cc: Matthew Wilcox (Oracle) Cc: Hsin-Yi Wang Cc: Xiongwei Song Signed-off-by: Andrew Morton --- fs/squashfs/zlib_wrapper.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'fs/squashfs/zlib_wrapper.c') diff --git a/fs/squashfs/zlib_wrapper.c b/fs/squashfs/zlib_wrapper.c index a20e9042146b..cbb7afe7bc46 100644 --- a/fs/squashfs/zlib_wrapper.c +++ b/fs/squashfs/zlib_wrapper.c @@ -62,6 +62,11 @@ static int zlib_uncompress(struct squashfs_sb_info *msblk, void *strm, stream->next_out = squashfs_first_page(output); stream->avail_in = 0; + if (IS_ERR(stream->next_out)) { + error = PTR_ERR(stream->next_out); + goto finish; + } + for (;;) { int zlib_err; @@ -85,7 +90,10 @@ static int zlib_uncompress(struct squashfs_sb_info *msblk, void *strm, if (stream->avail_out == 0) { stream->next_out = squashfs_next_page(output); - if (stream->next_out != NULL) + if (IS_ERR(stream->next_out)) { + error = PTR_ERR(stream->next_out); + break; + } else if (stream->next_out != NULL) stream->avail_out = PAGE_SIZE; } @@ -107,6 +115,7 @@ static int zlib_uncompress(struct squashfs_sb_info *msblk, void *strm, } } +finish: squashfs_finish_page(output); if (!error) @@ -122,6 +131,7 @@ const struct squashfs_decompressor squashfs_zlib_comp_ops = { .decompress = zlib_uncompress, .id = ZLIB_COMPRESSION, .name = "zlib", + .alloc_buffer = 1, .supported = 1 }; -- cgit v1.2.3