In article <1041555419.24901.86.camel@irongate.swansea.linux.org.uk>,
Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
>On Thu, 2003-01-02 at 23:16, David S. Miller wrote:
>>
>> With sendfile() all of this goes straight to the page cache directly
>> without a VMA lookup.
>
>With a nasty unpleasant splat the moment you do modification on the
>content at all. For static objects sendfile is certainly superior,
Oh, the "unpleasant splat" happens with the mmap approach too, there's
no avoiding it. It can happen with a regular "read()" loop too (if the
read happens at the wrong time).
Both mmap and sendfile have the issue that the "splat" can happen every
time, while a read() into a private area means that the splat can only
happen the first time the web server caches the content. But the read
into a private area is also obviously the worst one from a performance
standpoint.
There are two ways to avoid the splat:
- lock the file some way before reading/writing to it.
- do all updates to a temp-file, and move the temp-file to the new location.
Those two approaches will fix the "splat" problem _regardless_ of what
IO mechanism you use. With that in mind, sendfile() is clearly the one
that performs best by far, so..
Linus
-
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/
This archive was generated by hypermail 2b29 : Tue Jan 07 2003 - 22:00:20 EST