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![Phillip Lougher](/assets/img/avatar_default.png)
This introduces an implementation of squashfs_readpage_block() that directly decompresses into the page cache. This uses the previously added page handler abstraction to push down the necessary kmap_atomic/kunmap_atomic operations on the page cache buffers into the decompressors. This enables direct copying into the page cache without using the slow kmap/kunmap calls. The code detects when multiple threads are racing in squashfs_readpage() to decompress the same block, and avoids this regression by falling back to using an intermediate buffer. This patch enhances the performance of Squashfs significantly when multiple processes are accessing the filesystem simultaneously because it not only reduces memcopying, but it more importantly eliminates the lock contention on the intermediate buffer. Using single-thread decompression. dd if=file1 of=/dev/null bs=4096 & dd if=file2 of=/dev/null bs=4096 & dd if=file3 of=/dev/null bs=4096 & dd if=file4 of=/dev/null bs=4096 Before: 629145600 bytes (629 MB) copied, 45.8046 s, 13.7 MB/s After: 629145600 bytes (629 MB) copied, 9.29414 s, 67.7 MB/s Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk> Reviewed-by: Minchan Kim <minchan@kernel.org>
100 lines
2.6 KiB
C
100 lines
2.6 KiB
C
/*
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* Copyright (c) 2013
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* Phillip Lougher <phillip@squashfs.org.uk>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*/
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#include <linux/kernel.h>
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#include <linux/slab.h>
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#include <linux/pagemap.h>
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#include "page_actor.h"
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/*
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* This file contains implementations of page_actor for decompressing into
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* an intermediate buffer, and for decompressing directly into the
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* page cache.
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*
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* Calling code should avoid sleeping between calls to squashfs_first_page()
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* and squashfs_finish_page().
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*/
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/* Implementation of page_actor for decompressing into intermediate buffer */
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static void *cache_first_page(struct squashfs_page_actor *actor)
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{
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actor->next_page = 1;
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return actor->buffer[0];
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}
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static void *cache_next_page(struct squashfs_page_actor *actor)
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{
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if (actor->next_page == actor->pages)
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return NULL;
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return actor->buffer[actor->next_page++];
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}
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static void cache_finish_page(struct squashfs_page_actor *actor)
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{
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/* empty */
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}
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struct squashfs_page_actor *squashfs_page_actor_init(void **buffer,
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int pages, int length)
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{
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struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
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if (actor == NULL)
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return NULL;
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actor->length = length ? : pages * PAGE_CACHE_SIZE;
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actor->buffer = buffer;
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actor->pages = pages;
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actor->next_page = 0;
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actor->squashfs_first_page = cache_first_page;
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actor->squashfs_next_page = cache_next_page;
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actor->squashfs_finish_page = cache_finish_page;
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return actor;
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}
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/* Implementation of page_actor for decompressing directly into page cache. */
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static void *direct_first_page(struct squashfs_page_actor *actor)
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{
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actor->next_page = 1;
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return actor->pageaddr = kmap_atomic(actor->page[0]);
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}
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static void *direct_next_page(struct squashfs_page_actor *actor)
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{
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if (actor->pageaddr)
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kunmap_atomic(actor->pageaddr);
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return actor->pageaddr = actor->next_page == actor->pages ? NULL :
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kmap_atomic(actor->page[actor->next_page++]);
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}
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static void direct_finish_page(struct squashfs_page_actor *actor)
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{
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if (actor->pageaddr)
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kunmap_atomic(actor->pageaddr);
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}
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struct squashfs_page_actor *squashfs_page_actor_init_special(struct page **page,
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int pages, int length)
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{
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struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
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if (actor == NULL)
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return NULL;
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actor->length = length ? : pages * PAGE_CACHE_SIZE;
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actor->page = page;
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actor->pages = pages;
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actor->next_page = 0;
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actor->pageaddr = NULL;
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actor->squashfs_first_page = direct_first_page;
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actor->squashfs_next_page = direct_next_page;
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actor->squashfs_finish_page = direct_finish_page;
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return actor;
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}
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