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  1. 21 2月, 2006 1 次提交
    • K
      [PATCH] OOM kill: children accounting · 9827b781
      由 Kurt Garloff 提交于 
      In the badness() calculation, there's currently this piece of code:

        /*
         * Processes which fork a lot of child processes are likely
         * a good choice. We add the vmsize of the children if they
         * have an own mm. This prevents forking servers to flood the
         * machine with an endless amount of children
         */
        list_for_each(tsk, &p->children) {
                struct task_struct *chld;
                chld = list_entry(tsk, struct task_struct, sibling);
                if (chld->mm = p->mm && chld->mm)
                        points += chld->mm->total_vm;
        }

The intention is clear: If some server (apache) keeps spawning new children
and we run OOM, we want to kill the father rather than picking a child.

This -- to some degree -- also helps a bit with getting fork bombs under
control, though I'd consider this a desirable side-effect rather than a
feature.

There's one problem with this: No matter how many or few children there are,
if just one of them misbehaves, and all others (including the father) do
everything right, we still always kill the whole family.  This hits in real
life; whether it's javascript in konqueror resulting in kdeinit (and thus the
whole KDE session) being hit or just a classical server that spawns children.

Sidenote: The killer does kill all direct children as well, not only the
selected father, see oom_kill_process().

The idea in attached patch is that we do want to account the memory
consumption of the (direct) children to the father -- however not fully.
This maintains the property that fathers with too many children will still
very likely be picked, whereas a single misbehaving child has the chance to
be picked by the OOM killer.

In the patch I account only half (rounded up) of the children's vm_size to
the parent.  This means that if one child eats more mem than the rest of
the family, it will be picked, otherwise it's still the father and thus the
whole family that gets selected.

This is heuristics -- we could debate whether accounting for a fourth would
be better than for half of it.  Or -- if people would consider it worth the
trouble -- make it a sysctl.  For now I sticked to accounting for half,
which should IMHO be a significant improvement.

The patch does one more thing: As users tend to be irritated by the choice
of killed processes (mainly because the children are killed first, despite
some of them having a very low OOM score), I added some more output: The
selected (father) process will be reported first and it's oom_score printed
to syslog.

Description:

Only account for half of children's vm size in oom score calculation

This should still give the parent enough point in case of fork bombs.  If
any child however has more than 50% of the vm size of all children
together, it'll get a higher score and be elected.

This patch also makes the kernel display the oom_score.
Signed-off-by: NKurt Garloff <garloff@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      9827b781
  3. 18 2月, 2006 4 次提交
  5. 15 2月, 2006 3 次提交
    • M
      [PATCH] madvise MADV_DONTFORK/MADV_DOFORK · f8225661
      由 Michael S. Tsirkin 提交于 
      Currently, copy-on-write may change the physical address of a page even if the
user requested that the page is pinned in memory (either by mlock or by
get_user_pages).  This happens if the process forks meanwhile, and the parent
writes to that page.  As a result, the page is orphaned: in case of
get_user_pages, the application will never see any data hardware DMA's into
this page after the COW.  In case of mlock'd memory, the parent is not getting
the realtime/security benefits of mlock.

In particular, this affects the Infiniband modules which do DMA from and into
user pages all the time.

This patch adds madvise options to control whether memory range is inherited
across fork.  Useful e.g.  for when hardware is doing DMA from/into these
pages.  Could also be useful to an application wanting to speed up its forks
by cutting large areas out of consideration.
Signed-off-by: NMichael S. Tsirkin <mst@mellanox.co.il>
Acked-by: NHugh Dickins <hugh@veritas.com>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      f8225661
    • H
      [PATCH] compound page: default destructor · d98c7a09
      由 Hugh Dickins 提交于 
      Somehow I imagined that calling a NULL destructor would free a compound page
rather than oopsing.  No, we must supply a default destructor, __free_pages_ok
using the order noted by prep_compound_page.  hugetlb can still replace this
as before with its own free_huge_page pointer.

The case that needs this is not common: rarely does put_compound_page's
put_page_testzero bring the count down to 0.  But if get_user_pages is applied
to some part of a compound page, without immediate release (e.g.  AIO or
Infiniband), then it's possible for its put_page to come after the containing
vma has been unmapped and the driver done its free_pages.

That's just the kind of case compound pages are supposed to be guarding
against (but Nick points out, nor did PageReserved handle this right).
Signed-off-by: NHugh Dickins <hugh@veritas.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      d98c7a09
    • H
      [PATCH] compound page: use page[1].lru · 41d78ba5
      由 Hugh Dickins 提交于 
      If a compound page has its own put_page_testzero destructor (the only current
example is free_huge_page), that is noted in page[1].mapping of the compound
page.  But that's rather a poor place to keep it: functions which call
set_page_dirty_lock after get_user_pages (e.g.  Infiniband's
__ib_umem_release) ought to be checking first, otherwise set_page_dirty is
liable to crash on what's not the address of a struct address_space.

And now I'm about to make that worse: it turns out that every compound page
needs a destructor, so we can no longer rely on hugetlb pages going their own
special way, to avoid further problems of page->mapping reuse.  For example,
not many people know that: on 50% of i386 -Os builds, the first tail page of a
compound page purports to be PageAnon (when its destructor has an odd
address), which surprises page_add_file_rmap.

Keep the compound page destructor in page[1].lru.next instead.  And to free up
the common pairing of mapping and index, also move compound page order from
index to lru.prev.  Slab reuses page->lru too: but if we ever need slab to use
compound pages, it can easily stack its use above this.

(akpm: decoded version of the above: the tail pages of a compound page now
have ->mapping==NULL, so there's no need for the set_page_dirty[_lock]()
caller to check that they're not compund pages before doing the dirty).
Signed-off-by: NHugh Dickins <hugh@veritas.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      41d78ba5
  7. 12 2月, 2006 3 次提交
  9. 11 2月, 2006 2 次提交
  11. 08 2月, 2006 4 次提交
  13. 06 2月, 2006 6 次提交
  15. 05 2月, 2006 1 次提交
  17. 02 2月, 2006 16 次提交