Skip to content

L
linux
An error occurred fetching the project authors.
Switch branch/tag
  1. 04 Sep, 2015 1 commit
  3. 10 Jul, 2015 1 commit
    • Eric W. Biederman's avatar
      vfs: Commit to never having exectuables on proc and sysfs. · 90f8572b
      Eric W. Biederman authored 
      Today proc and sysfs do not contain any executable files.  Several
applications today mount proc or sysfs without noexec and nosuid and
then depend on there being no exectuables files on proc or sysfs.
Having any executable files show on proc or sysfs would cause
a user space visible regression, and most likely security problems.

Therefore commit to never allowing executables on proc and sysfs by
adding a new flag to mark them as filesystems without executables and
enforce that flag.

Test the flag where MNT_NOEXEC is tested today, so that the only user
visible effect will be that exectuables will be treated as if the
execute bit is cleared.

The filesystems proc and sysfs do not currently incoporate any
executable files so this does not result in any user visible effects.

This makes it unnecessary to vet changes to proc and sysfs tightly for
adding exectuable files or changes to chattr that would modify
existing files, as no matter what the individual file say they will
not be treated as exectuable files by the vfs.

Not having to vet changes to closely is important as without this we
are only one proc_create call (or another goof up in the
implementation of notify_change) from having problematic executables
on proc.  Those mistakes are all too easy to make and would create
a situation where there are security issues or the assumptions of
some program having to be broken (and cause userspace regressions).
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
      90f8572b
  5. 25 Jun, 2015 1 commit
  7. 15 Apr, 2015 2 commits
  9. 14 Apr, 2015 1 commit
  11. 25 Mar, 2015 1 commit
    • Leon Yu's avatar
      mm: fix anon_vma->degree underflow in anon_vma endless growing prevention · 3fe89b3e
      Leon Yu authored 
      I have constantly stumbled upon "kernel BUG at mm/rmap.c:399!" after
upgrading to 3.19 and had no luck with 4.0-rc1 neither.

So, after looking into new logic introduced by commit 7a3ef208 ("mm:
prevent endless growth of anon_vma hierarchy"), I found chances are that
unlink_anon_vmas() is called without incrementing dst->anon_vma->degree
in anon_vma_clone() due to allocation failure.  If dst->anon_vma is not
NULL in error path, its degree will be incorrectly decremented in
unlink_anon_vmas() and eventually underflow when exiting as a result of
another call to unlink_anon_vmas().  That's how "kernel BUG at
mm/rmap.c:399!" is triggered for me.

This patch fixes the underflow by dropping dst->anon_vma when allocation
fails.  It's safe to do so regardless of original value of dst->anon_vma
because dst->anon_vma doesn't have valid meaning if anon_vma_clone()
fails.  Besides, callers don't care dst->anon_vma in such case neither.

Also suggested by Michal Hocko, we can clean up vma_adjust() a bit as
anon_vma_clone() now does the work.

[akpm@linux-foundation.org: tweak comment]
Fixes: 7a3ef208 ("mm: prevent endless growth of anon_vma hierarchy")
Signed-off-by: default avatarLeon Yu <chianglungyu@gmail.com>
Signed-off-by: default avatarKonstantin Khlebnikov <koct9i@gmail.com>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarDavid Rientjes <rientjes@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      3fe89b3e
  13. 12 Feb, 2015 3 commits
    • Roman Gushchin's avatar
      mm/mmap.c: fix arithmetic overflow in __vm_enough_memory() · 5703b087
      Roman Gushchin authored 
      I noticed, that "allowed" can easily overflow by falling below 0,
because (total_vm / 32) can be larger than "allowed".  The problem
occurs in OVERCOMMIT_NONE mode.

In this case, a huge allocation can success and overcommit the system
(despite OVERCOMMIT_NONE mode).  All subsequent allocations will fall
(system-wide), so system become unusable.

The problem was masked out by commit c9b1d098
("mm: limit growth of 3% hardcoded other user reserve"),
but it's easy to reproduce it on older kernels:
1) set overcommit_memory sysctl to 2
2) mmap() large file multiple times (with VM_SHARED flag)
3) try to malloc() large amount of memory

It also can be reproduced on newer kernels, but miss-configured
sysctl_user_reserve_kbytes is required.

Fix this issue by switching to signed arithmetic here.

[akpm@linux-foundation.org: use min_t]
Signed-off-by: default avatarRoman Gushchin <klamm@yandex-team.ru>
Cc: Andrew Shewmaker <agshew@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      5703b087
    • Kirill A. Shutemov's avatar
      mm: fix false-positive warning on exit due mm_nr_pmds(mm) · b30fe6c7
      Kirill A. Shutemov authored 
      The problem is that we check nr_ptes/nr_pmds in exit_mmap() which happens
*before* pgd_free().  And if an arch does pte/pmd allocation in
pgd_alloc() and frees them in pgd_free() we see offset in counters by the
time of the checks.

We tried to workaround this by offsetting expected counter value according
to FIRST_USER_ADDRESS for both nr_pte and nr_pmd in exit_mmap().  But it
doesn't work in some cases:

1. ARM with LPAE enabled also has non-zero USER_PGTABLES_CEILING, but
   upper addresses occupied with huge pmd entries, so the trick with
   offsetting expected counter value will get really ugly: we will have
   to apply it nr_pmds, but not nr_ptes.

2. Metag has non-zero FIRST_USER_ADDRESS, but doesn't do allocation
   pte/pmd page tables allocation in pgd_alloc(), just setup a pgd entry
   which is allocated at boot and shared accross all processes.

The proposal is to move the check to check_mm() which happens *after*
pgd_free() and do proper accounting during pgd_alloc() and pgd_free()
which would bring counters to zero if nothing leaked.
Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: default avatarTyler Baker <tyler.baker@linaro.org>
Tested-by: default avatarTyler Baker <tyler.baker@linaro.org>
Tested-by: default avatarNishanth Menon <nm@ti.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      b30fe6c7
    • Kirill A. Shutemov's avatar
      mm: account pmd page tables to the process · dc6c9a35
      Kirill A. Shutemov authored 
      Dave noticed that unprivileged process can allocate significant amount of
memory -- >500 MiB on x86_64 -- and stay unnoticed by oom-killer and
memory cgroup.  The trick is to allocate a lot of PMD page tables.  Linux
kernel doesn't account PMD tables to the process, only PTE.

The use-cases below use few tricks to allocate a lot of PMD page tables
while keeping VmRSS and VmPTE low.  oom_score for the process will be 0.

	#include <errno.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <unistd.h>
	#include <sys/mman.h>
	#include <sys/prctl.h>

	#define PUD_SIZE (1UL << 30)
	#define PMD_SIZE (1UL << 21)

	#define NR_PUD 130000

	int main(void)
	{
		char *addr = NULL;
		unsigned long i;

		prctl(PR_SET_THP_DISABLE);
		for (i = 0; i < NR_PUD ; i++) {
			addr = mmap(addr + PUD_SIZE, PUD_SIZE, PROT_WRITE|PROT_READ,
					MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
			if (addr == MAP_FAILED) {
				perror("mmap");
				break;
			}
			*addr = 'x';
			munmap(addr, PMD_SIZE);
			mmap(addr, PMD_SIZE, PROT_WRITE|PROT_READ,
					MAP_ANONYMOUS|MAP_PRIVATE|MAP_FIXED, -1, 0);
			if (addr == MAP_FAILED)
				perror("re-mmap"), exit(1);
		}
		printf("PID %d consumed %lu KiB in PMD page tables\n",
				getpid(), i * 4096 >> 10);
		return pause();
	}

The patch addresses the issue by account PMD tables to the process the
same way we account PTE.

The main place where PMD tables is accounted is __pmd_alloc() and
free_pmd_range(). But there're few corner cases:

 - HugeTLB can share PMD page tables. The patch handles by accounting
   the table to all processes who share it.

 - x86 PAE pre-allocates few PMD tables on fork.

 - Architectures with FIRST_USER_ADDRESS > 0. We need to adjust sanity
   check on exit(2).

Accounting only happens on configuration where PMD page table's level is
present (PMD is not folded).  As with nr_ptes we use per-mm counter.  The
counter value is used to calculate baseline for badness score by
oom-killer.
Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Reviewed-by: default avatarCyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: David Rientjes <rientjes@google.com>
Tested-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      dc6c9a35
  15. 10 Feb, 2015 2 commits
    • Kirill A. Shutemov's avatar
      rmap: drop support of non-linear mappings · 27ba0644
      Kirill A. Shutemov authored 
      We don't create non-linear mappings anymore.  Let's drop code which
handles them in rmap.
Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      27ba0644
    • Kirill A. Shutemov's avatar
      mm: replace remap_file_pages() syscall with emulation · c8d78c18
      Kirill A. Shutemov authored 
      remap_file_pages(2) was invented to be able efficiently map parts of
huge file into limited 32-bit virtual address space such as in database
workloads.

Nonlinear mappings are pain to support and it seems there's no
legitimate use-cases nowadays since 64-bit systems are widely available.

Let's drop it and get rid of all these special-cased code.

The patch replaces the syscall with emulation which creates new VMA on
each remap_file_pages(), unless they it can be merged with an adjacent
one.

I didn't find *any* real code that uses remap_file_pages(2) to test
emulation impact on.  I've checked Debian code search and source of all
packages in ALT Linux.  No real users: libc wrappers, mentions in
strace, gdb, valgrind and this kind of stuff.

There are few basic tests in LTP for the syscall.  They work just fine
with emulation.

To test performance impact, I've written small test case which
demonstrate pretty much worst case scenario: map 4G shmfs file, write to
begin of every page pgoff of the page, remap pages in reverse order,
read every page.

The test creates 1 million of VMAs if emulation is in use, so I had to
set vm.max_map_count to 1100000 to avoid -ENOMEM.

Before:		23.3 ( +-  4.31% ) seconds
After:		43.9 ( +-  0.85% ) seconds
Slowdown:	1.88x

I believe we can live with that.

Test case:

        #define _GNU_SOURCE
        #include <assert.h>
        #include <stdlib.h>
        #include <stdio.h>
        #include <sys/mman.h>

        #define MB	(1024UL * 1024)
        #define SIZE	(4096 * MB)

        int main(int argc, char **argv)
        {
                unsigned long *p;
                long i, pass;

                for (pass = 0; pass < 10; pass++) {
                        p = mmap(NULL, SIZE, PROT_READ|PROT_WRITE,
                                        MAP_SHARED | MAP_ANONYMOUS, -1, 0);
                        if (p == MAP_FAILED) {
                                perror("mmap");
                                return -1;
                        }

                        for (i = 0; i < SIZE / 4096; i++)
                                p[i * 4096 / sizeof(*p)] = i;

                        for (i = 0; i < SIZE / 4096; i++) {
                                if (remap_file_pages(p + i * 4096 / sizeof(*p), 4096,
                                                0, (SIZE - 4096 * (i + 1)) >> 12, 0)) {
                                        perror("remap_file_pages");
                                        return -1;
                                }
                        }

                        for (i = SIZE / 4096 - 1; i >= 0; i--)
                                assert(p[i * 4096 / sizeof(*p)] == SIZE / 4096 - i - 1);

                        munmap(p, SIZE);
                }

                return 0;
        }

[akpm@linux-foundation.org: fix spello]
[sasha.levin@oracle.com: initialize populate before usage]
[sasha.levin@oracle.com: grab file ref to prevent race while mmaping]
Signed-off-by: default avatar"Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Dave Jones <davej@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Armin Rigo <arigo@tunes.org>
Signed-off-by: default avatarSasha Levin <sasha.levin@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      c8d78c18
  17. 11 Jan, 2015 2 commits
  19. 13 Dec, 2014 3 commits
  21. 03 Dec, 2014 1 commit
    • Daniel Forrest's avatar
      mm: fix anon_vma_clone() error treatment · c4ea95d7
      Daniel Forrest authored 
      Andrew Morton noticed that the error return from anon_vma_clone() was
being dropped and replaced with -ENOMEM (which is not itself a bug
because the only error return value from anon_vma_clone() is -ENOMEM).

I did an audit of callers of anon_vma_clone() and discovered an actual
bug where the error return was being lost.  In __split_vma(), between
Linux 3.11 and 3.12 the code was changed so the err variable is used
before the call to anon_vma_clone() and the default initial value of
-ENOMEM is overwritten.  So a failure of anon_vma_clone() will return
success since err at this point is now zero.

Below is a patch which fixes this bug and also propagates the error
return value from anon_vma_clone() in all cases.

Fixes: ef0855d3 ("mm: mempolicy: turn vma_set_policy() into vma_dup_policy()")
Signed-off-by: default avatarDaniel Forrest <dan.forrest@ssec.wisc.edu>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tim Hartrick <tim@edgecast.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>	[3.12+]
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      c4ea95d7
  23. 17 Nov, 2014 1 commit
    • Dave Hansen's avatar
      x86, mpx: Cleanup unused bound tables · 1de4fa14
      Dave Hansen authored 
      The previous patch allocates bounds tables on-demand.  As noted in
an earlier description, these can add up to *HUGE* amounts of
memory.  This has caused OOMs in practice when running tests.

This patch adds support for freeing bounds tables when they are no
longer in use.

There are two types of mappings in play when unmapping tables:
 1. The mapping with the actual data, which userspace is
    munmap()ing or brk()ing away, etc...
 2. The mapping for the bounds table *backing* the data
    (is tagged with VM_MPX, see the patch "add MPX specific
    mmap interface").

If userspace use the prctl() indroduced earlier in this patchset
to enable the management of bounds tables in kernel, when it
unmaps the first type of mapping with the actual data, the kernel
needs to free the mapping for the bounds table backing the data.
This patch hooks in at the very end of do_unmap() to do so.
We look at the addresses being unmapped and find the bounds
directory entries and tables which cover those addresses.  If
an entire table is unused, we clear associated directory entry
and free the table.

Once we unmap the bounds table, we would have a bounds directory
entry pointing at empty address space. That address space might
now be allocated for some other (random) use, and the MPX
hardware might now try to walk it as if it were a bounds table.
That would be bad.  So any unmapping of an enture bounds table
has to be accompanied by a corresponding write to the bounds
directory entry to invalidate it.  That write to the bounds
directory can fault, which causes the following problem:

Since we are doing the freeing from munmap() (and other paths
like it), we hold mmap_sem for write. If we fault, the page
fault handler will attempt to acquire mmap_sem for read and
we will deadlock.  To avoid the deadlock, we pagefault_disable()
when touching the bounds directory entry and use a
get_user_pages() to resolve the fault.

The unmapping of bounds tables happends under vm_munmap().  We
also (indirectly) call vm_munmap() to _do_ the unmapping of the
bounds tables.  We avoid unbounded recursion by disallowing
freeing of bounds tables *for* bounds tables.  This would not
occur normally, so should not have any practical impact.  Being
strict about it here helps ensure that we do not have an
exploitable stack overflow.
Based-on-patch-by: default avatarQiaowei Ren <qiaowei.ren@intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Cc: linux-mm@kvack.org
Cc: linux-mips@linux-mips.org
Cc: Dave Hansen <dave@sr71.net>
Link: http://lkml.kernel.org/r/20141114151831.E4531C4A@viggo.jf.intel.comSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      1de4fa14
  25. 29 Oct, 2014 1 commit
    • David Rientjes's avatar
      mm, thp: fix collapsing of hugepages on madvise · 6d50e60c
      David Rientjes authored 
      If an anonymous mapping is not allowed to fault thp memory and then
madvise(MADV_HUGEPAGE) is used after fault, khugepaged will never
collapse this memory into thp memory.

This occurs because the madvise(2) handler for thp, hugepage_madvise(),
clears VM_NOHUGEPAGE on the stack and it isn't stored in vma->vm_flags
until the final action of madvise_behavior().  This causes the
khugepaged_enter_vma_merge() to be a no-op in hugepage_madvise() when
the vma had previously had VM_NOHUGEPAGE set.

Fix this by passing the correct vma flags to the khugepaged mm slot
handler.  There's no chance khugepaged can run on this vma until after
madvise_behavior() returns since we hold mm->mmap_sem.

It would be possible to clear VM_NOHUGEPAGE directly from vma->vm_flags
in hugepage_advise(), but I didn't want to introduce special case
behavior into madvise_behavior().  I think it's best to just let it
always set vma->vm_flags itself.
Signed-off-by: default avatarDavid Rientjes <rientjes@google.com>
Reported-by: default avatarSuleiman Souhlal <suleiman@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      6d50e60c
  27. 14 Oct, 2014 1 commit
    • Peter Feiner's avatar
      mm: softdirty: enable write notifications on VMAs after VM_SOFTDIRTY cleared · 64e45507
      Peter Feiner authored 
      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 c9d0bf24 ("mm: uncached vma support with writenotify").
Signed-off-by: default avatarPeter Feiner <pfeiner@google.com>
Reported-by: default avatarPeter Feiner <pfeiner@google.com>
Suggested-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Jamie Liu <jamieliu@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      64e45507
  29. 10 Oct, 2014 5 commits
  31. 10 Sep, 2014 1 commit
  33. 08 Sep, 2014 1 commit
    • Tejun Heo's avatar
      percpu_counter: add @gfp to percpu_counter_init() · 908c7f19
      Tejun Heo authored 
      Percpu allocator now supports allocation mask.  Add @gfp to
percpu_counter_init() so that !GFP_KERNEL allocation masks can be used
with percpu_counters too.

We could have left percpu_counter_init() alone and added
percpu_counter_init_gfp(); however, the number of users isn't that
high and introducing _gfp variants to all percpu data structures would
be quite ugly, so let's just do the conversion.  This is the one with
the most users.  Other percpu data structures are a lot easier to
convert.

This patch doesn't make any functional difference.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarJan Kara <jack@suse.cz>
Acked-by: default avatar"David S. Miller" <davem@davemloft.net>
Cc: x86@kernel.org
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
      908c7f19
  35. 08 Aug, 2014 1 commit
    • David Herrmann's avatar
      mm: allow drivers to prevent new writable mappings · 4bb5f5d9
      David Herrmann authored 
      This patch (of 6):

The i_mmap_writable field counts existing writable mappings of an
address_space.  To allow drivers to prevent new writable mappings, make
this counter signed and prevent new writable mappings if it is negative.
This is modelled after i_writecount and DENYWRITE.

This will be required by the shmem-sealing infrastructure to prevent any
new writable mappings after the WRITE seal has been set.  In case there
exists a writable mapping, this operation will fail with EBUSY.

Note that we rely on the fact that iff you already own a writable mapping,
you can increase the counter without using the helpers.  This is the same
that we do for i_writecount.
Signed-off-by: default avatarDavid Herrmann <dh.herrmann@gmail.com>
Acked-by: default avatarHugh Dickins <hughd@google.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Ryan Lortie <desrt@desrt.ca>
Cc: Lennart Poettering <lennart@poettering.net>
Cc: Daniel Mack <zonque@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      4bb5f5d9
  37. 07 Aug, 2014 1 commit
  39. 06 Jun, 2014 1 commit
  41. 04 Jun, 2014 2 commits
  43. 20 May, 2014 1 commit
  45. 07 Apr, 2014 1 commit
    • Davidlohr Bueso's avatar
      mm: per-thread vma caching · 615d6e87
      Davidlohr Bueso authored 
      This patch is a continuation of efforts trying to optimize find_vma(),
avoiding potentially expensive rbtree walks to locate a vma upon faults.
The original approach (https://lkml.org/lkml/2013/11/1/410), where the
largest vma was also cached, ended up being too specific and random,
thus further comparison with other approaches were needed.  There are
two things to consider when dealing with this, the cache hit rate and
the latency of find_vma().  Improving the hit-rate does not necessarily
translate in finding the vma any faster, as the overhead of any fancy
caching schemes can be too high to consider.

We currently cache the last used vma for the whole address space, which
provides a nice optimization, reducing the total cycles in find_vma() by
up to 250%, for workloads with good locality.  On the other hand, this
simple scheme is pretty much useless for workloads with poor locality.
Analyzing ebizzy runs shows that, no matter how many threads are
running, the mmap_cache hit rate is less than 2%, and in many situations
below 1%.

The proposed approach is to replace this scheme with a small per-thread
cache, maximizing hit rates at a very low maintenance cost.
Invalidations are performed by simply bumping up a 32-bit sequence
number.  The only expensive operation is in the rare case of a seq
number overflow, where all caches that share the same address space are
flushed.  Upon a miss, the proposed replacement policy is based on the
page number that contains the virtual address in question.  Concretely,
the following results are seen on an 80 core, 8 socket x86-64 box:

1) System bootup: Most programs are single threaded, so the per-thread
   scheme does improve ~50% hit rate by just adding a few more slots to
   the cache.

+----------------+----------+------------------+
| caching scheme | hit-rate | cycles (billion) |
+----------------+----------+------------------+
| baseline       | 50.61%   | 19.90            |
| patched        | 73.45%   | 13.58            |
+----------------+----------+------------------+

2) Kernel build: This one is already pretty good with the current
   approach as we're dealing with good locality.

+----------------+----------+------------------+
| caching scheme | hit-rate | cycles (billion) |
+----------------+----------+------------------+
| baseline       | 75.28%   | 11.03            |
| patched        | 88.09%   | 9.31             |
+----------------+----------+------------------+

3) Oracle 11g Data Mining (4k pages): Similar to the kernel build workload.

+----------------+----------+------------------+
| caching scheme | hit-rate | cycles (billion) |
+----------------+----------+------------------+
| baseline       | 70.66%   | 17.14            |
| patched        | 91.15%   | 12.57            |
+----------------+----------+------------------+

4) Ebizzy: There's a fair amount of variation from run to run, but this
   approach always shows nearly perfect hit rates, while baseline is just
   about non-existent.  The amounts of cycles can fluctuate between
   anywhere from ~60 to ~116 for the baseline scheme, but this approach
   reduces it considerably.  For instance, with 80 threads:

+----------------+----------+------------------+
| caching scheme | hit-rate | cycles (billion) |
+----------------+----------+------------------+
| baseline       | 1.06%    | 91.54            |
| patched        | 99.97%   | 14.18            |
+----------------+----------+------------------+

[akpm@linux-foundation.org: fix nommu build, per Davidlohr]
[akpm@linux-foundation.org: document vmacache_valid() logic]
[akpm@linux-foundation.org: attempt to untangle header files]
[akpm@linux-foundation.org: add vmacache_find() BUG_ON]
[hughd@google.com: add vmacache_valid_mm() (from Oleg)]
[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: adjust and enhance comments]
Signed-off-by: default avatarDavidlohr Bueso <davidlohr@hp.com>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: default avatarMichel Lespinasse <walken@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Tested-by: default avatarHugh Dickins <hughd@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      615d6e87
  47. 03 Apr, 2014 1 commit
  49. 31 Mar, 2014 1 commit
  51. 18 Mar, 2014 1 commit
  53. 24 Jan, 2014 2 commits
    • Cyrill Gorcunov's avatar
      mm: ignore VM_SOFTDIRTY on VMA merging · 34228d47
      Cyrill Gorcunov authored 
      The VM_SOFTDIRTY bit affects vma merge routine: if two VMAs has all bits
in vm_flags matched except dirty bit the kernel can't longer merge them
and this forces the kernel to generate new VMAs instead.

It finally may lead to the situation when userspace application reaches
vm.max_map_count limit and get crashed in worse case

 | (gimp:11768): GLib-ERROR **: gmem.c:110: failed to allocate 4096 bytes
 |
 | (file-tiff-load:12038): LibGimpBase-WARNING **: file-tiff-load: gimp_wire_read(): error
 | xinit: connection to X server lost
 |
 | waiting for X server to shut down
 | /usr/lib64/gimp/2.0/plug-ins/file-tiff-load terminated: Hangup
 | /usr/lib64/gimp/2.0/plug-ins/script-fu terminated: Hangup
 | /usr/lib64/gimp/2.0/plug-ins/script-fu terminated: Hangup

  https://bugzilla.kernel.org/show_bug.cgi?id=67651
  https://bugzilla.gnome.org/show_bug.cgi?id=719619#c0

Initial problem came from missed VM_SOFTDIRTY in do_brk() routine but
even if we would set up VM_SOFTDIRTY here, there is still a way to
prevent VMAs from merging: one can call

 | echo 4 > /proc/$PID/clear_refs

and clear all VM_SOFTDIRTY over all VMAs presented in memory map, then
new do_brk() will try to extend old VMA and finds that dirty bit doesn't
match thus new VMA will be generated.

As discussed with Pavel, the right approach should be to ignore
VM_SOFTDIRTY bit when we're trying to merge VMAs and if merge successed
we mark extended VMA with dirty bit where needed.
Signed-off-by: default avatarCyrill Gorcunov <gorcunov@openvz.org>
Reported-by: default avatarBastian Hougaard <gnome@rvzt.net>
Reported-by: default avatarMel Gorman <mgorman@suse.de>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      34228d47
    • Paul Gortmaker's avatar
      mm: audit/fix non-modular users of module_init in core code · a64fb3cd
      Paul Gortmaker authored 
      Code that is obj-y (always built-in) or dependent on a bool Kconfig
(built-in or absent) can never be modular.  So using module_init as an
alias for __initcall can be somewhat misleading.

Fix these up now, so that we can relocate module_init from init.h into
module.h in the future.  If we don't do this, we'd have to add module.h
to obviously non-modular code, and that would be a worse thing.

The audit targets the following module_init users for change:
 mm/ksm.c                       bool KSM
 mm/mmap.c                      bool MMU
 mm/huge_memory.c               bool TRANSPARENT_HUGEPAGE
 mm/mmu_notifier.c              bool MMU_NOTIFIER

Note that direct use of __initcall is discouraged, vs.  one of the
priority categorized subgroups.  As __initcall gets mapped onto
device_initcall, our use of subsys_initcall (which makes sense for these
files) will thus change this registration from level 6-device to level
4-subsys (i.e.  slightly earlier).

However no observable impact of that difference has been observed during
testing.

One might think that core_initcall (l2) or postcore_initcall (l3) would
be more appropriate for anything in mm/ but if we look at some actual
init functions themselves, we see things like:

mm/huge_memory.c --> hugepage_init     --> hugepage_init_sysfs
mm/mmap.c        --> init_user_reserve --> sysctl_user_reserve_kbytes
mm/ksm.c         --> ksm_init          --> sysfs_create_group

and hence the choice of subsys_initcall (l4) seems reasonable, and at
the same time minimizes the risk of changing the priority too
drastically all at once.  We can adjust further in the future.

Also, several instances of missing ";" at EOL are fixed.
Signed-off-by: default avatarPaul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      a64fb3cd
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7