On Mon, 2 Jun 2014, Christoph Hellwig wrote: > On Mon, Jun 02, 2014 at 04:14:06PM +0200, Oleg Nesterov wrote: > > Ingo, please pull from > > > > git://git.kernel.org/pub/scm/linux/kernel/git/oleg/misc uprobes/core > > > > Based on tip:perf/uprobes > > Eww, adding tmpfs-specific code to uprobes screams layering violation. > > Hugh, what is the problem with implementing ->readpage for tmpfs again?
The problem is that ->readpage invites the caller to allocate a page of their choice for pagecache, and then pass it down to the filesystem to fill and use thereafter. There are several ways in which that does not suit tmpfs, 3 spring to mind: 1. the page may already be in memory, but currently in swapcache not in filecache: tmpfs knows how to manage that, the ->readpage caller does not 2. there may be a NUMA mempolicy applied to that file, which would choose to allocate the page differently: tmpfs knows about that, caller does not 3. (handy side-effect) it happens to disable use of tmpfs file as swapfile It was a great relief when tmpfs could finally jettison its ->readpage back in v3.1 (though if you press me, I could admit to some remaining embarrassments). I certainly do not want it back. Just think of tmpfs as a layering violation itself (memory as backing! no wonder it has peculiar demands on the allocation of its backing) and we're all good - there's a variety of ways in which the generic code already happens to accommodate it (many PageSwapBacked tests, or the mapping_cap_account_dirty/writeback tests, for example). IIRC, you were in on the discussion of shmem_read_mapping_page() when we introduced it: Oleg is simply adding a call to it to fix a uprobes bug. That the name explicitly mentions shmem instead of concealing it, is not necessarily a bad thing. Hugh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
