Messages in this thread | | | Date | 24 Nov 2005 12:48:43 -0500 | From | linux@horizon ... | Subject | Re: [patch] SMP alternatives |
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> I suspect that with MAP_SHARED + PROT_WRITE being pretty uncommon anyway, > we can probably find trivial patterns in the kernel. Like only one process > holding that file open - which is what you get with things that use mmap() > to write a new file (I think "ld" used to have a config option to write > files that way, for example).
Just a bit of practical experience: I use mmap() to write data a LOT, because msync(MS_ASYNC) is the most portable way to do an async write.
There are two applications. First, helping the OS not fill up with dirty pages. It's basically a way of saying "this page is not going to be dirtied again for a long time".
Secondly, to reduce the latency of synchronous writes. If I need to log operations durably, it helps to
1) fill the log pages, using MS_ASYNC as soon as the page is full 2) when committing a batch, use MS_SYNC to force data to disk 3) report batch successfully committed to stable storage
The aio_ routines are less widely supported some implementations have very high overhead. They would allow me to keep working while a commit is in progress, but the above is simple and reduces the burstiness of I/O considerably. - 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/
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