Messages in this thread | | | Date | Thu, 09 May 2002 06:13:11 -0700 (PDT) | Subject | Re: [PATCH] double flush_page_to_ram | From | "David S. Miller" <> |
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From: Andrea Arcangeli <andrea@suse.de> Date: Thu, 9 May 2002 15:21:16 +0200
The reason I did this patch is because it was functional equivalent to old 2.4 kernels.
in turn old 2.4 kernels were all wrong:
if (no_share) { struct page *new_page = alloc_page(GFP_HIGHUSER); if (new_page) { copy_user_highpage(new_page, old_page, address); flush_page_to_ram(new_page); } else new_page = NOPAGE_OOM; page_cache_release(page); return new_page; } flush_page_to_ram(old_page); return old_page; they don't flush old_page before the the memcpy, they only flush the _anon_ page _after_ the memcpy like current kernel with vm updates or Hugh's patch is doing (never the pagecache if it's an early cow).
filemap.c:filemap_nopage() does the flush in 2.4.x, what are you talking about?
It seems like moving the early cow into memory.c fixed the flush_page_to_ram bug by luck, because Hugh's patch is otherwise equivalent to old 2.4 kernels. Confirm? No it isn't. In 2.4.x kernels filemap_nopage does the flush just like it does now in 2.5.x What ancient 2.4.x sources are you looking at where filemap_nopage does not do the flush_page_to_ram right after the success: label?
If yes, I prefer to move the flush_page_to_ram on the _pagecache_ _before_ the memcpy into memory.c, it's cleaner if the pagecache layer doesn't need to care about cache aliasing between kernel direct mapping and userspace address space (but that it only cares about struct pages and filesystem, so only kernel side), and that such user-related part is covered only in memory.c. NO! The correct answer is to kill off flush_page_to_ram altogether. It is broken by design, and trying to make it work somehow "better" in 2.5.x is a losing game. We should make the ports fix up their stuff for a mechanism that we know _does_ work and that is flush_dcache_page plus {copy,clear}_user_page(). - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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