Block: Check major number before allocate the buffer in register_blkdev()
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From: Jens Axboe on 10 May 2010 08:40 Please don't top post when replying to emails, I fixed this one up for you. On Mon, May 10 2010, wzt wzt wrote: > On Mon, May 10, 2010 at 7:56 PM, Jens Axboe <jens.axboe(a)oracle.com> wrote: > > On Mon, May 10 2010, wzt.wzt(a)gmail.com wrote: > >> Check major number before allocate the buffer, if the major number is not exist, > >> and the register_blkdev() called many times, kmalloc()/kfree() will be no need > >> to invoked many times. So check the major number before use kmalloc() to allocate > >> the buffer will be better. > > > > This would generally be sound advice for performance oriented code, but > > I can't see it making any difference here. > > the original code use kmalloc() to allocate struct blk_major_name > buffer first, then find the major number in major_names array. if > found it, it will kfree() the unused struct blk_major_name buffer, > if register_blkdev() called many times like: > register_blkdev(22, "aa"); > .... > register_blkdev(22, "aa"); > kmalloc()/kfree() will be no need to invoked many times, my point is > that find the major number first, then allocate the buffer will be > better. this patch can handle the special case. Yes I realize how it works and what your patch does, my point is that it seems pointless to change code like that. Your 'test case' above isn't a valid one. If register_blkdev() was called tons of times per second and hence would be a hot code path, and it additionally most of the time ended up freeing the buffer, then there would be a case for changing it. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |