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/file_direct.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-) (limited to 'fs/squashfs/file_direct.c') diff --git a/fs/squashfs/file_direct.c b/fs/squashfs/file_direct.c index a4894cc59447..5af5802f5626 100644 --- a/fs/squashfs/file_direct.c +++ b/fs/squashfs/file_direct.c @@ -47,14 +47,6 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize, if (page == NULL) return res; - /* - * Create a "page actor" which will kmap and kunmap the - * page cache pages appropriately within the decompressor - */ - actor = squashfs_page_actor_init_special(page, pages, 0); - if (actor == NULL) - goto out; - /* Try to grab all the pages covered by the Squashfs block */ for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) { page[i] = (n == target_page->index) ? target_page : @@ -89,8 +81,19 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize, goto out; } + /* + * Create a "page actor" which will kmap and kunmap the + * page cache pages appropriately within the decompressor + */ + actor = squashfs_page_actor_init_special(msblk, page, pages, 0); + if (actor == NULL) + goto out; + /* Decompress directly into the page cache buffers */ res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor); + + kfree(actor); + if (res < 0) goto mark_errored; @@ -116,7 +119,6 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize, put_page(page[i]); } - kfree(actor); kfree(page); return 0; @@ -135,7 +137,6 @@ mark_errored: } out: - kfree(actor); kfree(page); return res; } -- cgit v1.2.3 From 1bb1a07afad97303f14b8d1b319b03f1f01a0091 Mon Sep 17 00:00:00 2001 From: Phillip Lougher Date: Sat, 11 Jun 2022 04:21:33 +0100 Subject: squashfs: don't use intermediate buffer if pages missing Now that the "page actor" can handle missing pages, we don't have to fall back to using an intermediate buffer in Squashfs_readpage_block() if all the pages necessary can't be obtained. Link: https://lkml.kernel.org/r/20220611032133.5743-3-phillip@squashfs.org.uk Signed-off-by: Phillip Lougher Cc: Hsin-Yi Wang Cc: Matthew Wilcox (Oracle) Cc: Xiongwei Song Signed-off-by: Andrew Morton --- fs/squashfs/file_direct.c | 75 ++++++++--------------------------------------- 1 file changed, 12 insertions(+), 63 deletions(-) (limited to 'fs/squashfs/file_direct.c') diff --git a/fs/squashfs/file_direct.c b/fs/squashfs/file_direct.c index 5af5802f5626..be4b12d31e0c 100644 --- a/fs/squashfs/file_direct.c +++ b/fs/squashfs/file_direct.c @@ -18,9 +18,6 @@ #include "squashfs.h" #include "page_actor.h" -static int squashfs_read_cache(struct page *target_page, u64 block, int bsize, - int pages, struct page **page, int bytes); - /* Read separately compressed datablock directly into page cache */ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize, int expected) @@ -33,7 +30,7 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize, int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1; int start_index = target_page->index & ~mask; int end_index = start_index | mask; - int i, n, pages, missing_pages, bytes, res = -ENOMEM; + int i, n, pages, bytes, res = -ENOMEM; struct page **page; struct squashfs_page_actor *actor; void *pageaddr; @@ -48,44 +45,29 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize, return res; /* Try to grab all the pages covered by the Squashfs block */ - for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) { + for (i = 0, n = start_index; n <= end_index; n++) { page[i] = (n == target_page->index) ? target_page : grab_cache_page_nowait(target_page->mapping, n); - if (page[i] == NULL) { - missing_pages++; + if (page[i] == NULL) continue; - } if (PageUptodate(page[i])) { unlock_page(page[i]); put_page(page[i]); - page[i] = NULL; - missing_pages++; + continue; } - } - - if (missing_pages) { - /* - * Couldn't get one or more pages, this page has either - * been VM reclaimed, but others are still in the page cache - * and uptodate, or we're racing with another thread in - * squashfs_readpage also trying to grab them. Fall back to - * using an intermediate buffer. - */ - res = squashfs_read_cache(target_page, block, bsize, pages, - page, expected); - if (res < 0) - goto mark_errored; - goto out; + i++; } + pages = i; + /* * Create a "page actor" which will kmap and kunmap the * page cache pages appropriately within the decompressor */ - actor = squashfs_page_actor_init_special(msblk, page, pages, 0); + actor = squashfs_page_actor_init_special(msblk, page, pages, expected); if (actor == NULL) goto out; @@ -102,12 +84,12 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize, goto mark_errored; } - /* Last page may have trailing bytes not filled */ + /* Last page (if present) may have trailing bytes not filled */ bytes = res % PAGE_SIZE; - if (bytes) { - pageaddr = kmap_atomic(page[pages - 1]); + if (page[pages - 1]->index == end_index && bytes) { + pageaddr = kmap_local_page(page[pages - 1]); memset(pageaddr + bytes, 0, PAGE_SIZE - bytes); - kunmap_atomic(pageaddr); + kunmap_local(pageaddr); } /* Mark pages as uptodate, unlock and release */ @@ -140,36 +122,3 @@ out: kfree(page); return res; } - - -static int squashfs_read_cache(struct page *target_page, u64 block, int bsize, - int pages, struct page **page, int bytes) -{ - struct inode *i = target_page->mapping->host; - struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb, - block, bsize); - int res = buffer->error, n, offset = 0; - - if (res) { - ERROR("Unable to read page, block %llx, size %x\n", block, - bsize); - goto out; - } - - for (n = 0; n < pages && bytes > 0; n++, - bytes -= PAGE_SIZE, offset += PAGE_SIZE) { - int avail = min_t(int, bytes, PAGE_SIZE); - - if (page[n] == NULL) - continue; - - squashfs_fill_page(page[n], buffer, offset, avail); - unlock_page(page[n]); - if (page[n] != target_page) - put_page(page[n]); - } - -out: - squashfs_cache_put(buffer); - return res; -} -- cgit v1.2.3