NFS: Optimise append writes with holes
If a file is being extended, and we're creating a hole, we might as well declare the entire page to be up to date. This patch significantly improves the write performance for sparse files in the case where lseek(SEEK_END) is used to append several non-contiguous writes at intervals of < PAGE_SIZE. Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
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@@ -344,6 +344,26 @@ static int nfs_write_end(struct file *file, struct address_space *mapping,
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unsigned offset = pos & (PAGE_CACHE_SIZE - 1);
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int status;
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/*
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* Zero any uninitialised parts of the page, and then mark the page
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* as up to date if it turns out that we're extending the file.
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*/
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if (!PageUptodate(page)) {
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unsigned pglen = nfs_page_length(page);
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unsigned end = offset + len;
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if (pglen == 0) {
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zero_user_segments(page, 0, offset,
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end, PAGE_CACHE_SIZE);
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SetPageUptodate(page);
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} else if (end >= pglen) {
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zero_user_segment(page, end, PAGE_CACHE_SIZE);
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if (offset == 0)
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SetPageUptodate(page);
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} else
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zero_user_segment(page, pglen, PAGE_CACHE_SIZE);
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}
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lock_kernel();
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status = nfs_updatepage(file, page, offset, copied);
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unlock_kernel();
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