Messages in this thread | | | Date | Sat, 3 Jan 1998 13:38:55 -0800 (PST) | From | Dean Gaudet <> | Subject | Re: 2.1.76, nfs client, and memory fragmentation |
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On Fri, 2 Jan 1998, Linus Torvalds wrote:
> One approach is to have just a "hint-map", which might indeed be good > enough. The hint-map would contain entries only for private un-shared > pages - which is often a large fraction of the pages. HOWEVER, I suspect > that the UNIX fork()/exec() semantics would make even this be impractical: > on average a lot of pages are not shared, but most pages are shared at > least for a short while every once in a while. And even if they become > unshared quickly after being shared, they will have lost the information > about what single mapping they had.
On a system running Apache there is a small set of pages that is shared between potentially hundreds of processes. I've seen httpds with SZ of 800k and SHARED of 720k on a particular busy server with 500 httpd children. This is a static-only server, on servers with a more dynamic mix the SZ will increase. On servers with mod_perl both SZ and SHARED can increase (there's more stuff which is constant after config time). In these cases the sharing stays in effect long after the fork().
Dean
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