Messages in this thread Patch in this message | | | From | "Fabio M. De Francesco" <> | Subject | [RFC PATCH] fs/isofs: Replace kmap() with kmap_local_page() | Date | Mon, 25 Jul 2022 18:23:31 +0200 |
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The use of kmap() is being deprecated in favor of kmap_local_page().
There are two main problems with kmap(): (1) It comes with an overhead as mapping space is restricted and protected by a global lock for synchronization and (2) it also requires global TLB invalidation when the kmap’s pool wraps and it might block when the mapping space is fully utilized until a slot becomes available.
With kmap_local_page() the mappings are per thread, CPU local, can take page faults, and can be called from any context (including interrupts). Tasks can be preempted and, when scheduled to run again, the kernel virtual addresses are restored and still valid. It is faster than kmap() in kernels with HIGHMEM enabled.
Since kmap_local_page() can be safely used in compress.c, it should be called everywhere instead of kmap().
Therefore, replace kmap() with kmap_local_page() in compress.c. Where it is needed, use memzero_page() instead of open coding kmap_local_page() plus memset() to fill the pages with zeros. Delete the redundant flush_dcache_page() in the two call sites of memzero_page().
This is an RFC because these changes have not been tested (tests are welcome!), therefore I'm not entirely sure whether these conversions work properly. I'd like to hear comments from more experienced developers before sending a real patch. Suggestions about how to run tests would also be much appreciated.
Suggested-by: Ira Weiny <ira.weiny@intel.com> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com> --- fs/isofs/compress.c | 24 +++++++++++++----------- 1 file changed, 13 insertions(+), 11 deletions(-)
diff --git a/fs/isofs/compress.c b/fs/isofs/compress.c index 95a19f25d61c..a1562124bb91 100644 --- a/fs/isofs/compress.c +++ b/fs/isofs/compress.c @@ -67,8 +67,7 @@ static loff_t zisofs_uncompress_block(struct inode *inode, loff_t block_start, for ( i = 0 ; i < pcount ; i++ ) { if (!pages[i]) continue; - memset(page_address(pages[i]), 0, PAGE_SIZE); - flush_dcache_page(pages[i]); + memzero_page(pages[i], 0, PAGE_SIZE); SetPageUptodate(pages[i]); } return ((loff_t)pcount) << PAGE_SHIFT; @@ -120,8 +119,7 @@ static loff_t zisofs_uncompress_block(struct inode *inode, loff_t block_start, zerr != Z_STREAM_END) { if (!stream.avail_out) { if (pages[curpage]) { - stream.next_out = page_address(pages[curpage]) - + poffset; + stream.next_out = kmap_local_page(pages[curpage] + poffset); stream.avail_out = PAGE_SIZE - poffset; poffset = 0; } else { @@ -170,6 +168,12 @@ static loff_t zisofs_uncompress_block(struct inode *inode, loff_t block_start, } } + if (stream.next_out) + if (stream.next_out != (char *)zisofs_sink_page) { + kunmap_local(stream.next_out); + stream.next_out = NULL; + } + if (!stream.avail_out) { /* This page completed */ if (pages[curpage]) { @@ -183,6 +187,9 @@ static loff_t zisofs_uncompress_block(struct inode *inode, loff_t block_start, } inflate_out: zlib_inflateEnd(&stream); + if (stream.next_out) + if (stream.next_out != (char *)zisofs_sink_page) + kunmap_local(stream.next_out); z_eio: mutex_unlock(&zisofs_zlib_lock); @@ -283,9 +290,7 @@ static int zisofs_fill_pages(struct inode *inode, int full_page, int pcount, } if (poffset && *pages) { - memset(page_address(*pages) + poffset, 0, - PAGE_SIZE - poffset); - flush_dcache_page(*pages); + memzero_page(*pages, poffset, PAGE_SIZE - poffset); SetPageUptodate(*pages); } return 0; @@ -343,10 +348,8 @@ static int zisofs_read_folio(struct file *file, struct folio *folio) for (i = 0; i < pcount; i++, index++) { if (i != full_page) pages[i] = grab_cache_page_nowait(mapping, index); - if (pages[i]) { + if (pages[i]) ClearPageError(pages[i]); - kmap(pages[i]); - } } err = zisofs_fill_pages(inode, full_page, pcount, pages); @@ -357,7 +360,6 @@ static int zisofs_read_folio(struct file *file, struct folio *folio) flush_dcache_page(pages[i]); if (i == full_page && err) SetPageError(pages[i]); - kunmap(pages[i]); unlock_page(pages[i]); if (i != full_page) put_page(pages[i]); -- 2.37.1
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