Messages in this thread | | | Date | Tue, 16 Jan 2007 03:41:14 +0000 | From | Jörn Engel <> | Subject | Re: O_DIRECT question |
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On Fri, 12 January 2007 00:19:45 +0800, Aubrey wrote: > > Yes for desktop, server, but maybe not for embedded system, specially > for no-mmu linux. In many embedded system cases, the whole system is > running in the ram, including file system. So it's not necessary using > page cache anymore. Page cache can't improve performance on these > cases, but only fragment memory.
You were not very specific, so I have to guess that you're referring to the problem of having two copies of the same file in RAM - one in the page cache and one in the "backing store", which is just RAM.
There are two solutions to this problem. One is tmpfs, which doesn't use a backing store and keeps all data in the page cache. The other is xip, which doesn't use the page cache and goes directly to backing store. Unlike O_DIRECT, xip only works with a RAM or de-facto RAM backing store (NOR flash works read-only).
So if you really care about memory waste in embedded systems, you should have a look at mm/filemap_xip.c and continue Carsten Otte's work.
Jörn
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