mm: restore KERNEL_DS optimisations
Restore the KERNEL_DS optimisation, especially helpful to the 2copy write path. This may be a pretty questionable gain in most cases, especially after the legacy 2copy write path is removed, but it doesn't cost much. Signed-off-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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1 changed files with 9 additions and 2 deletions
11
mm/filemap.c
11
mm/filemap.c
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@ -2061,7 +2061,7 @@ static ssize_t generic_perform_write_2copy(struct file *file,
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* cannot take a pagefault with the destination page locked.
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* So pin the source page to copy it.
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*/
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if (!PageUptodate(page)) {
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if (!PageUptodate(page) && !segment_eq(get_fs(), KERNEL_DS)) {
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unlock_page(page);
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src_page = alloc_page(GFP_KERNEL);
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@ -2186,6 +2186,13 @@ static ssize_t generic_perform_write(struct file *file,
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const struct address_space_operations *a_ops = mapping->a_ops;
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long status = 0;
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ssize_t written = 0;
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unsigned int flags = 0;
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/*
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* Copies from kernel address space cannot fail (NFSD is a big user).
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*/
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if (segment_eq(get_fs(), KERNEL_DS))
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flags |= AOP_FLAG_UNINTERRUPTIBLE;
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do {
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struct page *page;
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@ -2217,7 +2224,7 @@ static ssize_t generic_perform_write(struct file *file,
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break;
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}
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status = a_ops->write_begin(file, mapping, pos, bytes, 0,
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status = a_ops->write_begin(file, mapping, pos, bytes, flags,
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&page, &fsdata);
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if (unlikely(status))
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break;
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