linux/mm/memory.c, branch v3.18

mm: fix swapoff hang after page migration and fork

2014-12-03T17:36:03Z

I've been seeing swapoff hangs in recent testing: it's cycling around trying unsuccessfully to find an mm for some remaining pages of swap. I have been exercising swap and page migration more heavily recently, and now notice a long-standing error in copy_one_pte(): it's trying to add dst_mm to swapoff's mmlist when it finds a swap entry, but is doing so even when it's a migration entry or an hwpoison entry. Which wouldn't matter much, except it adds dst_mm next to src_mm, assuming src_mm is already on the mmlist: which may not be so. Then if pages are later swapped out from dst_mm, swapoff won't be able to find where to replace them. There's already a !non_swap_entry() test for stats: move that up before the swap_duplicate() and the addition to mmlist. Signed-off-by: Hugh Dickins Cc: Kelley Nielsen Cc: [2.6.18+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

zap_pte_range: update addr when forcing flush after TLB batching faiure

2014-10-28T20:16:28Z

When unmapping a range of pages in zap_pte_range, the page being unmapped is added to an mmu_gather_batch structure for asynchronous freeing. If we run out of space in the batch structure before the range has been completely unmapped, then we break out of the loop, force a TLB flush and free the pages that we have batched so far. If there are further pages to unmap, then we resume the loop where we left off. Unfortunately, we forget to update addr when we break out of the loop, which causes us to truncate the range being invalidated as the end address is exclusive. When we re-enter the loop at the same address, the page has already been freed and the pte_present test will fail, meaning that we do not reconsider the address for invalidation. This patch fixes the problem by incrementing addr by the PAGE_SIZE before breaking out of the loop on batch failure. Signed-off-by: Will Deacon Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds

mm: softdirty: enable write notifications on VMAs after VM_SOFTDIRTY cleared

2014-10-14T00:18:28Z

For VMAs that don't want write notifications, PTEs created for read faults have their write bit set. If the read fault happens after VM_SOFTDIRTY is cleared, then the PTE's softdirty bit will remain clear after subsequent writes. Here's a simple code snippet to demonstrate the bug: char* m = mmap(NULL, getpagesize(), PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED, -1, 0); system("echo 4 > /proc/$PPID/clear_refs"); /* clear VM_SOFTDIRTY */ assert(*m == '\0'); /* new PTE allows write access */ assert(!soft_dirty(x)); *m = 'x'; /* should dirty the page */ assert(soft_dirty(x)); /* fails */ With this patch, write notifications are enabled when VM_SOFTDIRTY is cleared. Furthermore, to avoid unnecessary faults, write notifications are disabled when VM_SOFTDIRTY is set. As a side effect of enabling and disabling write notifications with care, this patch fixes a bug in mprotect where vm_page_prot bits set by drivers were zapped on mprotect. An analogous bug was fixed in mmap by commit c9d0bf241451 ("mm: uncached vma support with writenotify"). Signed-off-by: Peter Feiner Reported-by: Peter Feiner Suggested-by: Kirill A. Shutemov Cc: Cyrill Gorcunov Cc: Pavel Emelyanov Cc: Jamie Liu Cc: Hugh Dickins Cc: Naoya Horiguchi Cc: Bjorn Helgaas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: softdirty: keep bit when zapping file pte

2014-09-26T15:10:35Z

This fixes the same bug as b43790eedd31 ("mm: softdirty: don't forget to save file map softdiry bit on unmap") and 9aed8614af5a ("mm/memory.c: don't forget to set softdirty on file mapped fault") where the return value of pte_*mksoft_dirty was being ignored. To be sure that no other pte/pmd "mk" function return values were being ignored, I annotated the functions in arch/x86/include/asm/pgtable.h with __must_check and rebuilt. The userspace effect of this bug is that the softdirty mark might be lost if a file mapped pte get zapped. Signed-off-by: Peter Feiner Acked-by: Cyrill Gorcunov Cc: Pavel Emelyanov Cc: Jamie Liu Cc: Hugh Dickins Cc: [3.12+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

2014-09-22T18:58:23Z

Pull KVM fixes from Paolo Bonzini: "Two very simple bugfixes, affecting all supported architectures" [ Two? There's three commits in here. Oh well, I guess Paolo didn't count the preparatory symbol export ] * tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: KVM: correct null pid check in kvm_vcpu_yield_to() KVM: check for !is_zero_pfn() in kvm_is_mmio_pfn() mm: export symbol dependencies of is_zero_pfn()

mm: export symbol dependencies of is_zero_pfn()

2014-09-14T14:25:14Z

In order to make the static inline function is_zero_pfn() callable by modules, export its symbol dependencies 'zero_pfn' and (for s390 and mips) 'zero_page_mask'. We need this for KVM, as CONFIG_KVM is a tristate for all supported architectures except ARM and arm64, and testing a pfn whether it refers to the zero page is required to correctly distinguish the zero page from other special RAM ranges that may also have the PG_reserved bit set, but need to be treated as MMIO memory. Signed-off-by: Ard Biesheuvel Acked-by: Andrew Morton Signed-off-by: Paolo Bonzini

x86,mm: fix pte_special versus pte_numa

2014-08-29T23:28:16Z

Sasha Levin has shown oopses on ffffea0003480048 and ffffea0003480008 at mm/memory.c:1132, running Trinity on different 3.16-rc-next kernels: where zap_pte_range() checks page->mapping to see if PageAnon(page). Those addresses fit struct pages for pfns d2001 and d2000, and in each dump a register or a stack slot showed d2001730 or d2000730: pte flags 0x730 are PCD ACCESSED PROTNONE SPECIAL IOMAP; and Sasha's e820 map has a hole between cfffffff and 100000000, which would need special access. Commit c46a7c817e66 ("x86: define _PAGE_NUMA by reusing software bits on the PMD and PTE levels") has broken vm_normal_page(): a PROTNONE SPECIAL pte no longer passes the pte_special() test, so zap_pte_range() goes on to try to access a non-existent struct page. Fix this by refining pte_special() (SPECIAL with PRESENT or PROTNONE) to complement pte_numa() (SPECIAL with neither PRESENT nor PROTNONE). A hint that this was a problem was that c46a7c817e66 added pte_numa() test to vm_normal_page(), and moved its is_zero_pfn() test from slow to fast path: This was papering over a pte_special() snag when the zero page was encountered during zap. This patch reverts vm_normal_page() to how it was before, relying on pte_special(). It still appears that this patch may be incomplete: aren't there other places which need to be handling PROTNONE along with PRESENT? For example, pte_mknuma() clears _PAGE_PRESENT and sets _PAGE_NUMA, but on a PROT_NONE area, that would make it pte_special(). This is side-stepped by the fact that NUMA hinting faults skipped PROT_NONE VMAs and there are no grounds where a NUMA hinting fault on a PROT_NONE VMA would be interesting. Fixes: c46a7c817e66 ("x86: define _PAGE_NUMA by reusing software bits on the PMD and PTE levels") Reported-by: Sasha Levin Tested-by: Sasha Levin Signed-off-by: Hugh Dickins Signed-off-by: Mel Gorman Cc: "Kirill A. Shutemov" Cc: Peter Zijlstra Cc: Rik van Riel Cc: Johannes Weiner Cc: Cyrill Gorcunov Cc: Matthew Wilcox Cc: [3.16] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

arm64,ia64,ppc,s390,sh,tile,um,x86,mm: remove default gate area

2014-08-08T22:57:27Z

The core mm code will provide a default gate area based on FIXADDR_USER_START and FIXADDR_USER_END if !defined(__HAVE_ARCH_GATE_AREA) && defined(AT_SYSINFO_EHDR). This default is only useful for ia64. arm64, ppc, s390, sh, tile, 64-bit UML, and x86_32 have their own code just to disable it. arm, 32-bit UML, and x86_64 have gate areas, but they have their own implementations. This gets rid of the default and moves the code into ia64. This should save some code on architectures without a gate area: it's now possible to inline the gate_area functions in the default case. Signed-off-by: Andy Lutomirski Acked-by: Nathan Lynch Acked-by: H. Peter Anvin Acked-by: Benjamin Herrenschmidt [in principle] Acked-by: Richard Weinberger [for um] Acked-by: Will Deacon [for arm64] Cc: Catalin Marinas Cc: Will Deacon Cc: Tony Luck Cc: Fenghua Yu Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Martin Schwidefsky Cc: Heiko Carstens Cc: Chris Metcalf Cc: Jeff Dike Cc: Richard Weinberger Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: Nathan Lynch Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: memcontrol: rewrite uncharge API

2014-08-08T22:57:17Z

The memcg uncharging code that is involved towards the end of a page's lifetime - truncation, reclaim, swapout, migration - is impressively complicated and fragile. Because anonymous and file pages were always charged before they had their page->mapping established, uncharges had to happen when the page type could still be known from the context; as in unmap for anonymous, page cache removal for file and shmem pages, and swap cache truncation for swap pages. However, these operations happen well before the page is actually freed, and so a lot of synchronization is necessary: - Charging, uncharging, page migration, and charge migration all need to take a per-page bit spinlock as they could race with uncharging. - Swap cache truncation happens during both swap-in and swap-out, and possibly repeatedly before the page is actually freed. This means that the memcg swapout code is called from many contexts that make no sense and it has to figure out the direction from page state to make sure memory and memory+swap are always correctly charged. - On page migration, the old page might be unmapped but then reused, so memcg code has to prevent untimely uncharging in that case. Because this code - which should be a simple charge transfer - is so special-cased, it is not reusable for replace_page_cache(). But now that charged pages always have a page->mapping, introduce mem_cgroup_uncharge(), which is called after the final put_page(), when we know for sure that nobody is looking at the page anymore. For page migration, introduce mem_cgroup_migrate(), which is called after the migration is successful and the new page is fully rmapped. Because the old page is no longer uncharged after migration, prevent double charges by decoupling the page's memcg association (PCG_USED and pc->mem_cgroup) from the page holding an actual charge. The new bits PCG_MEM and PCG_MEMSW represent the respective charges and are transferred to the new page during migration. mem_cgroup_migrate() is suitable for replace_page_cache() as well, which gets rid of mem_cgroup_replace_page_cache(). However, care needs to be taken because both the source and the target page can already be charged and on the LRU when fuse is splicing: grab the page lock on the charge moving side to prevent changing pc->mem_cgroup of a page under migration. Also, the lruvecs of both pages change as we uncharge the old and charge the new during migration, and putback may race with us, so grab the lru lock and isolate the pages iff on LRU to prevent races and ensure the pages are on the right lruvec afterward. Swap accounting is massively simplified: because the page is no longer uncharged as early as swap cache deletion, a new mem_cgroup_swapout() can transfer the page's memory+swap charge (PCG_MEMSW) to the swap entry before the final put_page() in page reclaim. Finally, page_cgroup changes are now protected by whatever protection the page itself offers: anonymous pages are charged under the page table lock, whereas page cache insertions, swapin, and migration hold the page lock. Uncharging happens under full exclusion with no outstanding references. Charging and uncharging also ensure that the page is off-LRU, which serializes against charge migration. Remove the very costly page_cgroup lock and set pc->flags non-atomically. [mhocko@suse.cz: mem_cgroup_charge_statistics needs preempt_disable] [vdavydov@parallels.com: fix flags definition] Signed-off-by: Johannes Weiner Cc: Hugh Dickins Cc: Tejun Heo Cc: Vladimir Davydov Tested-by: Jet Chen Acked-by: Michal Hocko Tested-by: Felipe Balbi Signed-off-by: Vladimir Davydov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: memcontrol: rewrite charge API

2014-08-08T22:57:17Z

These patches rework memcg charge lifetime to integrate more naturally with the lifetime of user pages. This drastically simplifies the code and reduces charging and uncharging overhead. The most expensive part of charging and uncharging is the page_cgroup bit spinlock, which is removed entirely after this series. Here are the top-10 profile entries of a stress test that reads a 128G sparse file on a freshly booted box, without even a dedicated cgroup (i.e. executing in the root memcg). Before: 15.36% cat [kernel.kallsyms] [k] copy_user_generic_string 13.31% cat [kernel.kallsyms] [k] memset 11.48% cat [kernel.kallsyms] [k] do_mpage_readpage 4.23% cat [kernel.kallsyms] [k] get_page_from_freelist 2.38% cat [kernel.kallsyms] [k] put_page 2.32% cat [kernel.kallsyms] [k] __mem_cgroup_commit_charge 2.18% kswapd0 [kernel.kallsyms] [k] __mem_cgroup_uncharge_common 1.92% kswapd0 [kernel.kallsyms] [k] shrink_page_list 1.86% cat [kernel.kallsyms] [k] __radix_tree_lookup 1.62% cat [kernel.kallsyms] [k] __pagevec_lru_add_fn After: 15.67% cat [kernel.kallsyms] [k] copy_user_generic_string 13.48% cat [kernel.kallsyms] [k] memset 11.42% cat [kernel.kallsyms] [k] do_mpage_readpage 3.98% cat [kernel.kallsyms] [k] get_page_from_freelist 2.46% cat [kernel.kallsyms] [k] put_page 2.13% kswapd0 [kernel.kallsyms] [k] shrink_page_list 1.88% cat [kernel.kallsyms] [k] __radix_tree_lookup 1.67% cat [kernel.kallsyms] [k] __pagevec_lru_add_fn 1.39% kswapd0 [kernel.kallsyms] [k] free_pcppages_bulk 1.30% cat [kernel.kallsyms] [k] kfree As you can see, the memcg footprint has shrunk quite a bit. text data bss dec hex filename 37970 9892 400 48262 bc86 mm/memcontrol.o.old 35239 9892 400 45531 b1db mm/memcontrol.o This patch (of 4): The memcg charge API charges pages before they are rmapped - i.e. have an actual "type" - and so every callsite needs its own set of charge and uncharge functions to know what type is being operated on. Worse, uncharge has to happen from a context that is still type-specific, rather than at the end of the page's lifetime with exclusive access, and so requires a lot of synchronization. Rewrite the charge API to provide a generic set of try_charge(), commit_charge() and cancel_charge() transaction operations, much like what's currently done for swap-in: mem_cgroup_try_charge() attempts to reserve a charge, reclaiming pages from the memcg if necessary. mem_cgroup_commit_charge() commits the page to the charge once it has a valid page->mapping and PageAnon() reliably tells the type. mem_cgroup_cancel_charge() aborts the transaction. This reduces the charge API and enables subsequent patches to drastically simplify uncharging. As pages need to be committed after rmap is established but before they are added to the LRU, page_add_new_anon_rmap() must stop doing LRU additions again. Revive lru_cache_add_active_or_unevictable(). [hughd@google.com: fix shmem_unuse] [hughd@google.com: Add comments on the private use of -EAGAIN] Signed-off-by: Johannes Weiner Acked-by: Michal Hocko Cc: Tejun Heo Cc: Vladimir Davydov Signed-off-by: Hugh Dickins Cc: Naoya Horiguchi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds