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req: Use kvzalloc() for allocating request map - #977
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For a large requests (several MiB and up) zalloc() has a huge chance to fail if the system memory is fragmented, causing I/O error. Prevent this error by using kvzalloc(), which internally first attempts zalloc(), and it it fails, falls back to vzmalloc(). For requests of that size the latency of the I/O itself is large enough for additional vmalloc allocation to not matter anyway, and for small requests we still have fast mempool/kmalloc path with a fallback. Signed-off-by: Robert Baldyga <robert.baldyga@unvertical.com>
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For a large requests (several MiB and up) zalloc() has a huge chance to fail if the system memory is fragmented, causing I/O error. Prevent this error by using kvzalloc(), which internally first attempts zalloc(), and it it fails, falls back to vzmalloc(). For requests of that size the latency of the I/O itself is large enough for additional vmalloc allocation to not matter anyway, and for small requests we still have fast mempool/kmalloc path with a fallback.