Messages in this thread | | | Subject | Re: [PATCH] cowlinks v2 | From | (Eric W. Biederman) | Date | 05 Apr 2004 03:15:01 -0600 |
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Jörn Engel <joern@wohnheim.fh-wedel.de> writes:
> On Sat, 3 April 2004 20:43:44 +0100, Jamie Lokier wrote: > > > > Btw, I'm not suggesting sharing page cache entries. > > But I am!!! > > Sharing the page cache is more important to me than sharing disk > space. Disk space is cheap, but increasing memory beyond 1GiB in my > notebook is not and 1GiB is too little, so memory is the real > constraint. > > And it looks like Pavel already found the solution. Whenever doing > something fishy that would confuse the page cache, we > 1. lock > 2. invalidate page cache for all files belonging to that cow entity > 3. copyfile(), write(), or whatever > 4. unlock > > This is always possibly, because page cache for cow-files is never > read-write. If it was, we would have done 1-4 before and now have a > regular (non-cow) file. > > Did I miss something?
I know a writable mmap needs to trigger a copy in that case. And then are fun cases with MAP_FIXED which may mean invalidation is not allowed.
As scheme that does not isolate the invalidate to the new copy worries me.
Eric
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