From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [RFC] page fault retry with NOPAGE_RETRY Date: Fri, 15 Sep 2006 23:35:39 +0200 References: <1158274508.14473.88.camel@localhost.localdomain> In-Reply-To: <1158274508.14473.88.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8BIT Content-Disposition: inline Message-Id: <200609152335.39960.arnd@arndb.de> Sender: owner-linux-mm@kvack.org Return-Path: To: Benjamin Herrenschmidt Cc: linux-mm@kvack.org, Linux Kernel list , Linus Torvalds List-ID: Am Friday 15 September 2006 00:55 schrieb Benjamin Herrenschmidt: > Somebody pointed to me that this might also be used to shoot another > bird, though I have not really though about it and wether it's good or > bad, which is the old problem of needing struct page for things that can > be mmap'ed. Using that trick, a driver could do the set_pte() itself in > the no_page handler and return NOPAGE_RETRY. I'm not sure about > advertising that feature though as I like all A callers of things like > set_pte() to be in well known locations, as there are various issues > related to manipulating the page tables that driver writers might not > get right. Though I suppose that if we consider the approach good, we > can provide a helper that "does the right thing" as well (like calling > update_mmu_cache(), flush_tlb_whatever(), etc...). One more point where it can help: When the backing store for the spufs mem file changes between vmalloc memory backed and pointing to a physical spu, we need to change vm_page_prot between (_PAGE_NO_CACHE | _PAGE_GUARDED) and the opposite. While all my investigations (with help from Hugh Dickins and Christoph Hellwig) show that it should be safe to do in the current code, the idea is still scary. When the nopage function for that file can simply return NOPAGE_RETRY after setting up the page tables, we don't need to worry about vm_page_prot any more. Arnd <>< -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org