Messages in this thread |  | | | Date | Fri, 5 Jan 2007 15:59:41 +0100 | | From | "Jesper Juhl" <> | | Subject | Re: open(O_DIRECT) on a tmpfs? |
| |
On 05/01/07, Jesper Juhl <jesper.juhl@gmail.com> wrote: > On 04/01/07, Hua Zhong <hzhong@gmail.com> wrote: > > > I see that as a good argument _not_ to allow O_DIRECT on > > > tmpfs, which inevitably impacts cache, even if O_DIRECT were > > > requested. > > > > > > But I'd also expect any app requesting O_DIRECT in that way, > > > as a caring citizen, to fall back to going without O_DIRECT > > > when it's not supported. > > > > According to "man 2 open" on my system: > > > > O_DIRECT > > Try to minimize cache effects of the I/O to and from this file. > > In general this will degrade performance, but it is useful in > > special situations, such as when applications do their own > > caching. File I/O is done directly to/from user space buffers. > > The I/O is synchronous, i.e., at the completion of the read(2) > > or write(2) system call, data is guaranteed to have been trans- > > ferred. Under Linux 2.4 transfer sizes, and the alignment of > > user buffer and file offset must all be multiples of the logi- > > cal block size of the file system. Under Linux 2.6 alignment to > > 512-byte boundaries suffices. > > A semantically similar interface for block devices is described > > in raw(8). > > > > This says nothing about (probably disk based) persistent backing store. I don't see why tmpfs has to conflict with it. > > > > So I'd argue that it makes more sense to support O_DIRECT on tmpfs as the memory IS the backing store. > > > > I'd agree. O_DIRECT means data will go direct to backing store, so if > RAM *is* the backing store as in the tmpfs case, then I see why > O_DIRECT should fail for it... > Whoops, that should of course have read " then I *DON'T* see why O_DIRECT should fail" .
-- Jesper Juhl <jesper.juhl@gmail.com> Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
|  |