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hpfs: optimize quad buffer loading
HPFS needs to load 4 consecutive 512-byte sectors when accessing the directory nodes or bitmaps. We can't switch to 2048-byte block size because files are allocated in the units of 512-byte sectors. Previously, the driver would allocate a 2048-byte area using kmalloc, copy the data from four buffers to this area and eventually copy them back if they were modified. In the current implementation of the buffer cache, buffers are allocated in the pagecache. That means that 4 consecutive 512-byte buffers are stored in consecutive areas in the kernel address space. So, we don't need to allocate extra memory and copy the content of the buffers there. This patch optimizes the code to avoid copying the buffers. It checks if the four buffers are stored in contiguous memory - if they are not, it falls back to allocating a 2048-byte area and copying data there. Signed-off-by: Mikulas Patocka <firstname.lastname@example.org> Signed-off-by: Linus Torvalds <email@example.com>
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