Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933138Ab3FFMoI (ORCPT ); Thu, 6 Jun 2013 08:44:08 -0400 Received: from merlin.infradead.org ([205.233.59.134]:47340 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932817Ab3FFMoF (ORCPT ); Thu, 6 Jun 2013 08:44:05 -0400 Date: Thu, 6 Jun 2013 14:43:51 +0200 From: Peter Zijlstra To: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org, roland@kernel.org, mingo@kernel.org, tglx@linutronix.de, kosaki.motohiro@gmail.com, penberg@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-rdma@vger.kernel.org Subject: [PATCH] mm: Revert pinned_vm braindamage Message-ID: <20130606124351.GZ27176@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10780 Lines: 273 Patch bc3e53f682 ("mm: distinguish between mlocked and pinned pages") broke RLIMIT_MEMLOCK. Before that patch: mm_struct::locked_vm < RLIMIT_MEMLOCK; after that patch we have: mm_struct::locked_vm < RLIMIT_MEMLOCK && mm_struct::pinned_vm < RLIMIT_MEMLOCK. The patch doesn't mention RLIMIT_MEMLOCK and thus also doesn't discus this (user visible) change in semantics. And thus we must assume it was unintentional. Since RLIMIT_MEMLOCK is very clearly a limit on the amount of pages the process can 'lock' into memory it should very much include pinned pages as well as mlock()ed pages. Neither can be paged. Since nobody had anything constructive to say about the VM_PINNED approach and the IB code hurts my head too much to make it work I propose we revert said patch. Once again the rationale; MLOCK(2) is part of POSIX Realtime Extentsion (1003.1b-1993/1003.1i-1995). It states that the specified part of the user address space should stay memory resident until either program exit or a matching munlock() call. This definition basically excludes major faults from happening on the pages -- a major fault being one where IO needs to happen to obtain the page content; the direct implication being that page content must remain in memory. Linux has taken this literal and made mlock()ed pages subject to page migration (albeit only for the explicit move_pages() syscall; but it would very much like to make them subject to implicit page migration for the purpose of compaction etc.). This view disregards the intention of the spec; since mlock() is part of the realtime spec the intention is very much that the user address range generate no faults; neither minor nor major -- any delay is unacceptable. This leaves the RT people unhappy -- therefore _if_ we continue with this Linux specific interpretation of mlock() we must introduce new syscalls that implement the intended mlock() semantics. It was found that there are useful purposes for this weaker mlock(), a rationale to indeed have two sets of syscalls. The weaker mlock() can be used in the context of security -- where we avoid sensitive data being written to disk, and in the context of userspace deamons that are part of the IO path -- which would otherwise form IO deadlocks. The proposed second set of primitives would be mpin() and munpin() and would implement the intended mlock() semantics. Such pages would not be migratable in any way (a possible implementation would be to 'pin' the pages using an extra refcount on the page frame). From the above we can see that any mpin()ed page is also an mlock()ed page, since mpin() will disallow any fault, and thus will also disallow major faults. While we still lack the formal mpin() and munpin() syscalls there are a number of sites that have similar 'side effects' and result in user controlled 'pinning' of pages. Namely IB and perf. For the purpose of RLIMIT_MEMLOCK we must use intent only as it is not part of the formal spec. The only useful thing is to limit the amount of pages a user can exempt from paging. This would therefore include all pages either mlock()ed or mpin()ed. Back to the patch; a resource limit must have a resource counter to enact the limit upon. Before the patch this was mm_struct::locked_vm. After the patch there is no such thing left. The patch was proposed to 'fix' a double accounting problem where pages are both pinned and mlock()ed. This was particularly visible when using mlockall() on a process that uses either IB or perf. I state that since mlockall() disables/invalidates RLIMIT_MEMLOCK the actual resource counter value is irrelevant, and thus the reported problem is a non-problem. However, it would still be possible to observe weirdness in the very unlikely event that a user would indeed call mlock() upon an address range obtained from IB/perf. In this case he would be unduly constrained and find his effective RLIMIT_MEMLOCK limit halved (at worst). After the patch; that same user will find he has an effectively double RLIMIT_MEMLOCK, since the IB/perf pages are not counted towards the same limit as his mlock() pages are. It is far more likely a user will employ mlock() on different rages than those he received from IB/perf since he already knows those aren't going anywhere. Therefore the patch trades an unlikely weirdness for a much more likely weirdness. So barring a proper solution I propose we revert. I've yet to hear a coherent objection to the above. Christoph is always quick to yell: 'but if fixes a double accounting issue' but is completely deaf to the fact that he changed user visible semantics without mention and regard. Signed-off-by: Peter Zijlstra --- drivers/infiniband/core/umem.c | 8 ++++---- drivers/infiniband/hw/ipath/ipath_user_pages.c | 6 +++--- drivers/infiniband/hw/qib/qib_user_pages.c | 4 ++-- fs/proc/task_mmu.c | 2 -- include/linux/mm_types.h | 1 - kernel/events/core.c | 6 +++--- 6 files changed, 12 insertions(+), 15 deletions(-) diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c index a841123..cc92137b 100644 --- a/drivers/infiniband/core/umem.c +++ b/drivers/infiniband/core/umem.c @@ -137,7 +137,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr, down_write(¤t->mm->mmap_sem); - locked = npages + current->mm->pinned_vm; + locked = npages + current->mm->locked_vm; lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT; if ((locked > lock_limit) && !capable(CAP_IPC_LOCK)) { @@ -207,7 +207,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr, __ib_umem_release(context->device, umem, 0); kfree(umem); } else - current->mm->pinned_vm = locked; + current->mm->locked_vm = locked; up_write(¤t->mm->mmap_sem); if (vma_list) @@ -223,7 +223,7 @@ static void ib_umem_account(struct work_struct *work) struct ib_umem *umem = container_of(work, struct ib_umem, work); down_write(&umem->mm->mmap_sem); - umem->mm->pinned_vm -= umem->diff; + umem->mm->locked_vm -= umem->diff; up_write(&umem->mm->mmap_sem); mmput(umem->mm); kfree(umem); @@ -269,7 +269,7 @@ void ib_umem_release(struct ib_umem *umem) } else down_write(&mm->mmap_sem); - current->mm->pinned_vm -= diff; + current->mm->locked_vm -= diff; up_write(&mm->mmap_sem); mmput(mm); kfree(umem); diff --git a/drivers/infiniband/hw/ipath/ipath_user_pages.c b/drivers/infiniband/hw/ipath/ipath_user_pages.c index dc66c45..cfed539 100644 --- a/drivers/infiniband/hw/ipath/ipath_user_pages.c +++ b/drivers/infiniband/hw/ipath/ipath_user_pages.c @@ -79,7 +79,7 @@ static int __ipath_get_user_pages(unsigned long start_page, size_t num_pages, goto bail_release; } - current->mm->pinned_vm += num_pages; + current->mm->locked_vm += num_pages; ret = 0; goto bail; @@ -178,7 +178,7 @@ void ipath_release_user_pages(struct page **p, size_t num_pages) __ipath_release_user_pages(p, num_pages, 1); - current->mm->pinned_vm -= num_pages; + current->mm->locked_vm -= num_pages; up_write(¤t->mm->mmap_sem); } @@ -195,7 +195,7 @@ static void user_pages_account(struct work_struct *_work) container_of(_work, struct ipath_user_pages_work, work); down_write(&work->mm->mmap_sem); - work->mm->pinned_vm -= work->num_pages; + work->mm->locked_vm -= work->num_pages; up_write(&work->mm->mmap_sem); mmput(work->mm); kfree(work); diff --git a/drivers/infiniband/hw/qib/qib_user_pages.c b/drivers/infiniband/hw/qib/qib_user_pages.c index 2bc1d2b..7689e49 100644 --- a/drivers/infiniband/hw/qib/qib_user_pages.c +++ b/drivers/infiniband/hw/qib/qib_user_pages.c @@ -74,7 +74,7 @@ static int __qib_get_user_pages(unsigned long start_page, size_t num_pages, goto bail_release; } - current->mm->pinned_vm += num_pages; + current->mm->locked_vm += num_pages; ret = 0; goto bail; @@ -151,7 +151,7 @@ void qib_release_user_pages(struct page **p, size_t num_pages) __qib_release_user_pages(p, num_pages, 1); if (current->mm) { - current->mm->pinned_vm -= num_pages; + current->mm->locked_vm -= num_pages; up_write(¤t->mm->mmap_sem); } } diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 3e636d8..7d09d6a 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -44,7 +44,6 @@ void task_mem(struct seq_file *m, struct mm_struct *mm) "VmPeak:\t%8lu kB\n" "VmSize:\t%8lu kB\n" "VmLck:\t%8lu kB\n" - "VmPin:\t%8lu kB\n" "VmHWM:\t%8lu kB\n" "VmRSS:\t%8lu kB\n" "VmData:\t%8lu kB\n" @@ -56,7 +55,6 @@ void task_mem(struct seq_file *m, struct mm_struct *mm) hiwater_vm << (PAGE_SHIFT-10), total_vm << (PAGE_SHIFT-10), mm->locked_vm << (PAGE_SHIFT-10), - mm->pinned_vm << (PAGE_SHIFT-10), hiwater_rss << (PAGE_SHIFT-10), total_rss << (PAGE_SHIFT-10), data << (PAGE_SHIFT-10), diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index ace9a5f..d185c13 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -356,7 +356,6 @@ struct mm_struct { unsigned long total_vm; /* Total pages mapped */ unsigned long locked_vm; /* Pages that have PG_mlocked set */ - unsigned long pinned_vm; /* Refcount permanently increased */ unsigned long shared_vm; /* Shared pages (files) */ unsigned long exec_vm; /* VM_EXEC & ~VM_WRITE */ unsigned long stack_vm; /* VM_GROWSUP/DOWN */ diff --git a/kernel/events/core.c b/kernel/events/core.c index 95edd5a..1e926b2 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -3729,7 +3729,7 @@ static void perf_mmap_close(struct vm_area_struct *vma) if (ring_buffer_put(rb)) { atomic_long_sub((size >> PAGE_SHIFT) + 1, &mmap_user->locked_vm); - vma->vm_mm->pinned_vm -= mmap_locked; + vma->vm_mm->locked_vm -= mmap_locked; free_uid(mmap_user); } } @@ -3805,7 +3805,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) lock_limit = rlimit(RLIMIT_MEMLOCK); lock_limit >>= PAGE_SHIFT; - locked = vma->vm_mm->pinned_vm + extra; + locked = vma->vm_mm->locked_vm + extra; if ((locked > lock_limit) && perf_paranoid_tracepoint_raw() && !capable(CAP_IPC_LOCK)) { @@ -3831,7 +3831,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) rb->mmap_user = get_current_user(); atomic_long_add(user_extra, &user->locked_vm); - vma->vm_mm->pinned_vm += extra; + vma->vm_mm->locked_vm += extra; rcu_assign_pointer(event->rb, rb); -- 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/