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Date: Tue, 27 Mar 2007 11:23:06 +0200 From: Miklos Szeredi <miklos@...redi.hu> To: akpm@...ux-foundation.org CC: a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: Re: [patch resend v4] update ctime and mtime for mmaped write > > > > But Peter Staubach says a RH custumer has files written thorugh mmap, > > > > which are not being backed up. > > > > > > Yes, I expect the backup problem is the major real-world hurt arising from > > > this bug. > > > > > > But I expect we could adequately plug that problem at munmap()-time. Or, > > > better, do_wp_page(). As I said - half-assed. > > > > > > It's a question if whether the backup problem is the only thing which is hurting > > > in the real-world, or if people have other problems. > > > > > > (In fact, what's wrong with doing it in do_wp_page()? > > > > It's rather more expensive, than just toggling a bit. > > It shouldn't be, especially for filesystems which have one-second timestamp > granularity. > > Filesystems which have s_time_gran=1 might hurt a bit, but no more than > they will with write(). > > Actually, no - we'd only update the mctime once per page per writeback > period (30 seconds by default) so the load will be small. Why? For each faulted page the times will be updated, no? Maybe it's acceptable, I don't really know the cost of file_update_time(). Tried this patch, and it seems to work. It will even randomly update the time for tmpfs files (on initial fault, and on swapins). Miklos Index: linux/mm/memory.c =================================================================== --- linux.orig/mm/memory.c 2007-03-27 11:04:40.000000000 +0200 +++ linux/mm/memory.c 2007-03-27 11:08:19.000000000 +0200 @@ -1664,6 +1664,8 @@ gotten: unlock: pte_unmap_unlock(page_table, ptl); if (dirty_page) { + if (vma->vm_file) + file_update_time(vma->vm_file); set_page_dirty_balance(dirty_page); put_page(dirty_page); } @@ -2316,6 +2318,8 @@ retry: unlock: pte_unmap_unlock(page_table, ptl); if (dirty_page) { + if (vma->vm_file) + file_update_time(vma->vm_file); set_page_dirty_balance(dirty_page); put_page(dirty_page); } - 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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