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Date: Thu, 9 Aug 2007 23:15:42 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Dean Nelson <dcn@....com> Cc: linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, tony.luck@...el.com, jes@....com Subject: Re: [RFC 3/3] SGI Altix cross partition memory (XPMEM) On Thu, 9 Aug 2007 20:14:35 -0500 Dean Nelson <dcn@....com> wrote: > This patch provides cross partition access to user memory (XPMEM) when > running multiple partitions on a single SGI Altix. > - Please don't send multiple patches all with the same title. - Feed the diff through checkpatch.pl, ponder the result. - Avoid needless casts to and from void* (eg, vm_private_data) - The test for PF_DUMPCORE in xpmem_fault_handler() is mysterious and merits a comment. - xpmem_fault_handler() is scary. - xpmem_fault_handler() appears to have imposed a kernel-wide rule that when taking multiple mmap_sems, one should take the lowest-addressed one first? If so, that probably wants a mention in that locking comment in filemap.c - xpmem_fault_handler() does atomic_dec(&seg_tg->mm->mm_users). What happens if that was the last reference? - Has it all been tested with lockdep enabled? Jugding from all the use of SPIN_LOCK_UNLOCKED, it has not. Oh, ia64 doesn't implement lockdep. For this code, that is deeply regrettable. - This code all predates the nopage->fault conversion and won't work in current kernels. - xpmem_attach() does smp_processor_id() in preemptible code. Lucky that ia64 doesn't do preempt? - Stuff like this: + ap_tg = xpmem_tg_ref_by_apid(apid); + if (IS_ERR(ap_tg)) + return PTR_ERR(ap_tg); + + ap = xpmem_ap_ref_by_apid(ap_tg, apid); + if (IS_ERR(ap)) { + xpmem_tg_deref(ap_tg); + return PTR_ERR(ap); + } is fragile. It is easy to introduce leaks and locking errors as the code evolves. The code has a lot of these deeply-embedded `return' statments preceded by duplicated unwinding. Kenrel code generally prefers to do the `goto out' thing. - "XPMEM_FLAG_VALIDPTEs"? Someone's pinky got tired at the end ;) Attention span expired at 19%, sorry. It's a large patch. - 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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