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Date: Fri, 15 Sep 2006 11:38:41 +0800 From: "Yingchao Zhou" <yc_zhou@...c.ac.cn> To: "Hugh Dickins" <hugh@...itas.com> Cc: "linux-kernel" <linux-kernel@...r.kernel.org>, "akpm" <akpm@...l.org>, "alan" <alan@...hat.com>, "zxc" <zxc@...c.ac.cn> Subject: Re: Re: Re: [RFC] PAGE_RW Should be added to PAGE_COPY ? >On Fri, 15 Sep 2006, Yingchao Zhou wrote: >> > >> >You want to mmap MAP_SHARED, which will use PAGE_SHARED instead, >> >including the write bit, both before and after the mprotects. >> >There should be no problem then: do you actually see a problem >> >when MAP_SHARED is used? >> It's ok to mmap MAP_SHARED. But is it not a normal way to malloc() a space and >> then registered to NIC ? > >Not that I know of. How would one register malloc()ed space to a NIC? >Sorry, I may well be misunderstanding you. The user-level NIC does this, eg. Myrinet... > >> >> Adding PAGE_RW to PAGE_COPY will resolve this problem. >> > >> >No! That would give every user write access to shared files they >> >should have no write access to. >> I guess you refer to mmap a file MAP_READ|MAP_WRITE in MAP_PRIVATE way. >> I think it is probably more logical to read the file data into an anoymous page and filled the pte with _PAGE_RW in the first time page-fault. It will probably reduce numbers of page fault interrupt. > >do_no_page() does just that when its fault demands write access; but >doesn't waste memory and time on copying when it's only a read access. > Yeah, it is. But this is the source of the problem described above. >Hugh > Yingchao Zhou - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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