Because of page order checks in __alloc_pages(), hugepage (and similarly
large order) allocations will not retry unless explicitly marked
__GFP_REPEAT. However, the current retry logic is nearly an infinite
loop (or until reclaim does no progress whatsoever). For these costly
allocations, that seems like overkill and could potentially never
terminate. Mel observed that allowing current __GFP_REPEAT semantics for
hugepage allocations essentially killed the system. I believe this is
because we may continue to reclaim small orders of pages all over, but
never have enough to satisfy the hugepage allocation request. This is
clearly only a problem for large order allocations, of which hugepages
are the most obvious (to me).
Modify try_to_free_pages() to indicate how many pages were reclaimed.
Use that information in __alloc_pages() to eventually fail a large
__GFP_REPEAT allocation when we've reclaimed an order of pages equal to
or greater than the allocation's order. This relies on lumpy reclaim
functioning as advertised. Due to fragmentation, lumpy reclaim may not
be able to free up the order needed in one invocation, so multiple
iterations may be requred. In other words, the more fragmented memory
is, the more retry attempts __GFP_REPEAT will make (particularly for
higher order allocations).
This changes the semantics of __GFP_REPEAT subtly, but *only* for
allocations > PAGE_ALLOC_COSTLY_ORDER. With this patch, for those size
allocations, we will try up to some point (at least 1<<order reclaimed
pages), rather than forever (which is the case for allocations <=
PAGE_ALLOC_COSTLY_ORDER).
This change improves the /proc/sys/vm/nr_hugepages interface with a
follow-on patch that makes pool allocations use __GFP_REPEAT. Rather
than administrators repeatedly echo'ing a particular value into the
sysctl, and forcing reclaim into action manually, this change allows for
the sysctl to attempt a reasonable effort itself. Similarly, dynamic
pool growth should be more successful under load, as lumpy reclaim can
try to free up pages, rather than failing right away.
Choosing to reclaim only up to the order of the requested allocation
strikes a balance between not failing hugepage allocations and returning
to the caller when it's unlikely to every succeed. Because of lumpy
reclaim, if we have freed the order requested, hopefully it has been in
big chunks and those chunks will allow our allocation to succeed. If
that isn't the case after freeing up the current order, I don't think it
is likely to succeed in the future, although it is possible given a
particular fragmentation pattern.
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Tested-by: Mel Gorman <mel@csn.ul.ie>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Filtering zonelists requires very frequent use of zone_idx(). This is costly
as it involves a lookup of another structure and a substraction operation. As
the zone_idx is often required, it should be quickly accessible. The node idx
could also be stored here if it was found that accessing zone->node is
significant which may be the case on workloads where nodemasks are heavily
used.
This patch introduces a struct zoneref to store a zone pointer and a zone
index. The zonelist then consists of an array of these struct zonerefs which
are looked up as necessary. Helpers are given for accessing the zone index as
well as the node index.
[kamezawa.hiroyu@jp.fujitsu.com: Suggested struct zoneref instead of embedding information in pointers]
[hugh@veritas.com: mm-have-zonelist: fix memcg ooms]
[hugh@veritas.com: just return do_try_to_free_pages]
[hugh@veritas.com: do_try_to_free_pages gfp_mask redundant]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Christoph Lameter <clameter@sgi.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Currently a node has two sets of zonelists, one for each zone type in the
system and a second set for GFP_THISNODE allocations. Based on the zones
allowed by a gfp mask, one of these zonelists is selected. All of these
zonelists consume memory and occupy cache lines.
This patch replaces the multiple zonelists per-node with two zonelists. The
first contains all populated zones in the system, ordered by distance, for
fallback allocations when the target/preferred node has no free pages. The
second contains all populated zones in the node suitable for GFP_THISNODE
allocations.
An iterator macro is introduced called for_each_zone_zonelist() that interates
through each zone allowed by the GFP flags in the selected zonelist.
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The following patches replace multiple zonelists per node with two zonelists
that are filtered based on the GFP flags. The patches as a set fix a bug with
regard to the use of MPOL_BIND and ZONE_MOVABLE. With this patchset, the
MPOL_BIND will apply to the two highest zones when the highest zone is
ZONE_MOVABLE. This should be considered as an alternative fix for the
MPOL_BIND+ZONE_MOVABLE in 2.6.23 to the previously discussed hack that filters
only custom zonelists.
The first patch cleans up an inconsistency where direct reclaim uses
zonelist->zones where other places use zonelist.
The second patch introduces a helper function node_zonelist() for looking up
the appropriate zonelist for a GFP mask which simplifies patches later in the
set.
The third patch defines/remembers the "preferred zone" for numa statistics, as
it is no longer always the first zone in a zonelist.
The forth patch replaces multiple zonelists with two zonelists that are
filtered. The two zonelists are due to the fact that the memoryless patchset
introduces a second set of zonelists for __GFP_THISNODE.
The fifth patch introduces helper macros for retrieving the zone and node
indices of entries in a zonelist.
The final patch introduces filtering of the zonelists based on a nodemask.
Two zonelists exist per node, one for normal allocations and one for
__GFP_THISNODE.
Performance results varied depending on the machine configuration. In real
workloads the gain/loss will depend on how much the userspace portion of the
benchmark benefits from having more cache available due to reduced referencing
of zonelists.
These are the range of performance losses/gains when running against
2.6.24-rc4-mm1. The set and these machines are a mix of i386, x86_64 and
ppc64 both NUMA and non-NUMA.
loss to gain
Total CPU time on Kernbench: -0.86% to 1.13%
Elapsed time on Kernbench: -0.79% to 0.76%
page_test from aim9: -4.37% to 0.79%
brk_test from aim9: -0.71% to 4.07%
fork_test from aim9: -1.84% to 4.60%
exec_test from aim9: -0.71% to 1.08%
This patch:
The allocator deals with zonelists which indicate the order in which zones
should be targeted for an allocation. Similarly, direct reclaim of pages
iterates over an array of zones. For consistency, this patch converts direct
reclaim to use a zonelist. No functionality is changed by this patch. This
simplifies zonelist iterators in the next patch.
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Use new node_to_cpumask_ptr. This creates a pointer to the
cpumask for a given node. This definition is in mm patch:
asm-generic-add-node_to_cpumask_ptr-macro.patch
* Use new set_cpus_allowed_ptr function.
Depends on:
[mm-patch]: asm-generic-add-node_to_cpumask_ptr-macro.patch
[sched-devel]: sched: add new set_cpus_allowed_ptr function
[x86/latest]: x86: add cpus_scnprintf function
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Greg Banks <gnb@melbourne.sgi.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Revert commit f1a9ee758d:
Author: Rik van Riel <riel@redhat.com>
Date: Thu Feb 7 00:14:08 2008 -0800
kswapd should only wait on IO if there is IO
The current kswapd (and try_to_free_pages) code has an oddity where the
code will wait on IO, even if there is no IO in flight. This problem is
notable especially when the system scans through many unfreeable pages,
causing unnecessary stalls in the VM.
Additionally, tasks without __GFP_FS or __GFP_IO in the direct reclaim path
will sleep if a significant number of pages are encountered that should be
written out. This gives kswapd a chance to write out those pages, while
the direct reclaim task sleeps.
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Because of large latencies and interactivity problems reported by Carlos,
here: http://lkml.org/lkml/2008/3/22/211
Cc: Rik van Riel <riel@redhat.com>
Cc: "Carlos R. Mafra" <crmafra2@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Rename Memory Controller to Memory Resource Controller. Reflect the same
changes in the CONFIG definition for the Memory Resource Controller. Group
together the config options for Resource Counters and Memory Resource
Controller.
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
When using memory controller, there are 2 levels of memory reclaim.
1. zone memory reclaim because of system/zone memory shortage.
2. memory cgroup memory reclaim because of hitting limit.
These two can be distinguished by sc->mem_cgroup parameter.
(scan_global_lru() macro)
This patch tries to make memory cgroup reclaim routine avoid affecting
system/zone memory reclaim. This patch inserts if (scan_global_lru()) and
hook to memory_cgroup reclaim support functions.
This patch can be a help for isolating system lru activity and group lru
activity and shows what additional functions are necessary.
* mem_cgroup_calc_mapped_ratio() ... calculate mapped ratio for cgroup.
* mem_cgroup_reclaim_imbalance() ... calculate active/inactive balance in
cgroup.
* mem_cgroup_calc_reclaim_active() ... calculate the number of active pages to
be scanned in this priority in mem_cgroup.
* mem_cgroup_calc_reclaim_inactive() ... calculate the number of inactive pages
to be scanned in this priority in mem_cgroup.
* mem_cgroup_all_unreclaimable() .. checks cgroup's page is all unreclaimable
or not.
* mem_cgroup_get_reclaim_priority() ...
* mem_cgroup_note_reclaim_priority() ... record reclaim priority (temporal)
* mem_cgroup_remember_reclaim_priority()
.... record reclaim priority as
zone->prev_priority.
This value is used for calc reclaim_mapped.
[akpm@linux-foundation.org: fix unused var warning]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Paul Menage <menage@google.com>
Cc: Pavel Emelianov <xemul@openvz.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Because NODE_DATA(node)->node_zonelists[] is guaranteed to contain all
necessary zones, it is not necessary to use for_each_online_node.
And this for_each_online_node() makes reclaim routine start always
from node 0. This is not good. This patch makes reclaim start from
caller's node and just use usual (default) zonelist order.
[akpm@linux-foundation.org: fix warning]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelianov <xemul@openvz.org>
Cc: Paul Menage <menage@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: David Rientjes <rientjes@google.com>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The current kswapd (and try_to_free_pages) code has an oddity where the
code will wait on IO, even if there is no IO in flight. This problem is
notable especially when the system scans through many unfreeable pages,
causing unnecessary stalls in the VM.
Additionally, tasks without __GFP_FS or __GFP_IO in the direct reclaim path
will sleep if a significant number of pages are encountered that should be
written out. This gives kswapd a chance to write out those pages, while
the direct reclaim task sleeps.
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Nick Piggin pointed out that swap cache and page cache addition routines
could be called from non GFP_KERNEL contexts. This patch makes the
charging routine aware of the gfp context. Charging might fail if the
cgroup is over it's limit, in which case a suitable error is returned.
This patch was tested on a Powerpc box. I am still looking at being able
to test the path, through which allocations happen in non GFP_KERNEL
contexts.
[kamezawa.hiroyu@jp.fujitsu.com: problem with ZONE_MOVABLE]
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelianov <xemul@openvz.org>
Cc: Paul Menage <menage@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: David Rientjes <rientjes@google.com>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Add the page_cgroup to the per cgroup LRU. The reclaim algorithm has
been modified to make the isolate_lru_pages() as a pluggable component. The
scan_control data structure now accepts the cgroup on behalf of which
reclaims are carried out. try_to_free_pages() has been extended to become
cgroup aware.
[akpm@linux-foundation.org: fix warning]
[Lee.Schermerhorn@hp.com: initialize all scan_control's isolate_pages member]
[bunk@kernel.org: make do_try_to_free_pages() static]
[hugh@veritas.com: memcgroup: fix try_to_free order]
[kamezawa.hiroyu@jp.fujitsu.com: this unlock_page_cgroup() is unnecessary]
Signed-off-by: Pavel Emelianov <xemul@openvz.org>
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: David Rientjes <rientjes@google.com>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Get rid of sparse related warnings from places that use integer as NULL
pointer.
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Cc: Andi Kleen <ak@suse.de>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Ian Kent <raven@themaw.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Introduces new zone flag interface for testing and setting flags:
int zone_test_and_set_flag(struct zone *zone, zone_flags_t flag)
Instead of setting and clearing ZONE_RECLAIM_LOCKED each time shrink_zone() is
called, this flag is test and set before starting zone reclaim. Zone reclaim
starts in __alloc_pages() when a zone's watermark fails and the system is in
zone_reclaim_mode. If it's already in reclaim, there's no need to start again
so it is simply considered full for that allocation attempt.
There is a change of behavior with regard to concurrent zone shrinking. It is
now possible for try_to_free_pages() or kswapd to already be shrinking a
particular zone when __alloc_pages() starts zone reclaim. In this case, it is
possible for two concurrent threads to invoke shrink_zone() for a single zone.
This change forbids a zone to be in zone reclaim twice, which was always the
behavior, but allows for concurrent try_to_free_pages() or kswapd shrinking
when starting zone reclaim.
Cc: Andrea Arcangeli <andrea@suse.de>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Convert the int all_unreclaimable member of struct zone to unsigned long
flags. This can now be used to specify several different zone flags such as
all_unreclaimable and reclaim_in_progress, which can now be removed and
converted to a per-zone flag.
Flags are set and cleared as follows:
zone_set_flag(struct zone *zone, zone_flags_t flag)
zone_clear_flag(struct zone *zone, zone_flags_t flag)
Defines the first zone flags, ZONE_ALL_UNRECLAIMABLE and ZONE_RECLAIM_LOCKED,
which have the same semantics as the old zone->all_unreclaimable and
zone->reclaim_in_progress, respectively. Also converts all current users that
set or clear either flag to use the new interface.
Helper functions are defined to test the flags:
int zone_is_all_unreclaimable(const struct zone *zone)
int zone_is_reclaim_locked(const struct zone *zone)
All flag operators are of the atomic variety because there are currently
readers that are implemented that do not take zone->lock.
[akpm@linux-foundation.org: add needed include]
Cc: Andrea Arcangeli <andrea@suse.de>
Acked-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Swappiness isn't a safe sysctl. Setting it to 0 for example can hang a
system. That's a corner case but even setting it to 10 or lower can waste
enormous amounts of cpu without making much progress. We've customers who
wants to use swappiness but they can't because of the current
implementation (if you change it so the system stops swapping it really
stops swapping and nothing works sane anymore if you really had to swap
something to make progress).
This patch from Kurt Garloff makes swappiness safer to use (no more huge
cpu usage or hangs with low swappiness values).
I think the prev_priority can also be nuked since it wastes 4 bytes per
zone (that would be an incremental patch but I wait the nr_scan_[in]active
to be nuked first for similar reasons). Clearly somebody at some point
noticed how broken that thing was and they had to add min(priority,
prev_priority) to give it some reliability, but they didn't go the last
mile to nuke prev_priority too. Calculating distress only in function of
not-racy priority is correct and sure more than enough without having to
add randomness into the equation.
Patch is tested on older kernels but it compiles and it's quite simple
so...
Overall I'm not very satisified by the swappiness tweak, since it doesn't
rally do anything with the dirty pagecache that may be inactive. We need
another kind of tweak that controls the inactive scan and tunes the
can_writepage feature (not yet in mainline despite having submitted it a
few times), not only the active one. That new tweak will tell the kernel
how hard to scan the inactive list for pure clean pagecache (something the
mainline kernel isn't capable of yet). We already have that feature
working in all our enterprise kernels with the default reasonable tune, or
they can't even run a readonly backup with tar without triggering huge
write I/O. I think it should be available also in mainline later.
Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: Kurt Garloff <garloff@suse.de>
Signed-off-by: Andrea Arcangeli <andrea@suse.de>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
When a cpu is onlined on memory-less-node box, kernel panics due to touch
NULL pointer of pgdat->kswapd. Current kswapd runs only nodes which have
memory. So, calling of set_cpus_allowed() is not necessary for memory-less
node.
This is fix for it.
Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We need the check for a node with cpu in zone reclaim. Zone reclaim will not
allow remote zone reclaim if a node has a cpu.
[Lee.Schermerhorn@hp.com: Move setup of N_CPU node state mask]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Tested-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Acked-by: Bob Picco <bob.picco@hp.com>
Cc: Nishanth Aravamudan <nacc@us.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mel@skynet.ie>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The current VM can get itself into trouble fairly easily on systems with a
small ZONE_HIGHMEM, which is common on i686 computers with 1GB of memory.
On one side, page_alloc() will allocate down to zone->pages_low, while on
the other side, kswapd() and balance_pgdat() will try to free memory from
every zone, until every zone has more free pages than zone->pages_high.
Highmem can be filled up to zone->pages_low with page tables, ramfs,
vmalloc allocations and other unswappable things quite easily and without
many bad side effects, since we still have a huge ZONE_NORMAL to do future
allocations from.
However, as long as the number of free pages in the highmem zone is below
zone->pages_high, kswapd will continue swapping things out from
ZONE_NORMAL, too!
Sami Farin managed to get his system into a stage where kswapd had freed
about 700MB of low memory and was still "going strong".
The attached patch will make kswapd stop paging out data from zones when
there is more than enough memory free. We do go above zone->pages_high in
order to keep pressure between zones equal in normal circumstances, but the
patch should prevent the kind of excesses that made Sami's computer totally
unusable.
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
