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Date: Tue, 29 Oct 2019 15:14:59 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: David Rientjes <rientjes@...gle.com>
Cc: Michal Hocko <mhocko@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrea Arcangeli <aarcange@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mel Gorman <mgorman@...e.de>,
"Kirill A. Shutemov" <kirill@...temov.name>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>
Subject: Re: [patch for-5.3 0/4] revert immediate fallback to remote hugepages
On 10/24/19 8:59 PM, David Rientjes wrote:
>> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
>> index 4ae967bcf954..2c48146f3ee2 100644
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -2129,18 +2129,20 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
>> nmask = policy_nodemask(gfp, pol);
>> if (!nmask || node_isset(hpage_node, *nmask)) {
>> mpol_cond_put(pol);
>> + /*
>> + * First, try to allocate THP only on local node, but
>> + * don't reclaim unnecessarily, just compact.
>> + */
>> page = __alloc_pages_node(hpage_node,
>> - gfp | __GFP_THISNODE, order);
>> + gfp | __GFP_THISNODE | __GFP_NORETRY, order);
>>
>> /*
>> - * If hugepage allocations are configured to always
>> - * synchronous compact or the vma has been madvised
>> - * to prefer hugepage backing, retry allowing remote
>> - * memory as well.
>> + * If that fails, allow both compaction and reclaim,
>> + * but on all nodes.
>> */
>> - if (!page && (gfp & __GFP_DIRECT_RECLAIM))
>> + if (!page)
>> page = __alloc_pages_node(hpage_node,
>> - gfp | __GFP_NORETRY, order);
>> + gfp, order);
>>
>> goto out;
>> }
> Hi Vlastimil,
>
> For the default case where thp enabled is not set to "always" and the VMA
I assume you meant "defrag" instead of "enabled".
> is not madvised for MADV_HUGEPAGE, how does this prefer to return node
> local pages rather than remote hugepages? The idea is to optimize for
> access latency when the vma has not been explicitly madvised.
Right, you mentioned this before IIRC, and I forgot. How about this?
We could be also smarter and consolidate to a single attempt if there's
actually just a single NUMA node, but that can be optimized later.
----8<----
>From 4c3a2217d0ee5ead00b1443010d07c664b6ac645 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@...e.cz>
Date: Tue, 1 Oct 2019 14:20:58 +0200
Subject: [PATCH] mm, thp: tweak reclaim/compaction effort of local-only and
all-node allocations
THP page faults now attempt a __GFP_THISNODE allocation first, which should
only compact existing free memory, followed by another attempt that can
allocate from any node using reclaim/compaction effort specified by global
defrag setting and madvise.
This patch makes the following changes to the scheme:
- before the patch, the first allocation relies on a check for pageblock order
and __GFP_IO to prevent excessive reclaim. This however affects also the
second attempt, which is not limited to single node. Instead of that, reuse
the existing check for costly order __GFP_NORETRY allocations, and make sure
the first THP attempt uses __GFP_NORETRY. As a side-effect, all costly order
__GFP_NORETRY allocations will bail out if compaction needs reclaim, while
previously they only bailed out when compaction was deferred due to previous
failures. This should be still acceptable within the __GFP_NORETRY semantics.
- before the patch, the second allocation attempt (on all nodes) was passing
__GFP_NORETRY. This is redundant as the check for pageblock order (discussed
above) was stronger. It's also contrary to madvise(MADV_HUGEPAGE) which means
some effort to allocate THP is requested. After this patch, the second
attempt doesn't pass __GFP_THISNODE nor __GFP_NORETRY.
To sum up, THP page faults now try the following attempts:
1. local node only THP allocation with no reclaim, just compaction.
2. for madvised VMA's or when synchronous compaction is enabled always - THP
allocation from any node with effort determined by global defrag setting
and VMA madvise
3. fallback to base pages on any node
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
mm/mempolicy.c | 10 +++++++---
mm/page_alloc.c | 24 +++++-------------------
2 files changed, 12 insertions(+), 22 deletions(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 4ae967bcf954..ed6fbc5b1e20 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2129,18 +2129,22 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
nmask = policy_nodemask(gfp, pol);
if (!nmask || node_isset(hpage_node, *nmask)) {
mpol_cond_put(pol);
+ /*
+ * First, try to allocate THP only on local node, but
+ * don't reclaim unnecessarily, just compact.
+ */
page = __alloc_pages_node(hpage_node,
- gfp | __GFP_THISNODE, order);
+ gfp | __GFP_THISNODE | __GFP_NORETRY, order);
/*
* If hugepage allocations are configured to always
* synchronous compact or the vma has been madvised
* to prefer hugepage backing, retry allowing remote
- * memory as well.
+ * memory with both reclaim and compact as well.
*/
if (!page && (gfp & __GFP_DIRECT_RECLAIM))
page = __alloc_pages_node(hpage_node,
- gfp | __GFP_NORETRY, order);
+ gfp, order);
goto out;
}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ecc3dbad606b..36d7d852f7b1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4473,8 +4473,11 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
if (page)
goto got_pg;
- if (order >= pageblock_order && (gfp_mask & __GFP_IO) &&
- !(gfp_mask & __GFP_RETRY_MAYFAIL)) {
+ /*
+ * Checks for costly allocations with __GFP_NORETRY, which
+ * includes some THP page fault allocations
+ */
+ if (costly_order && (gfp_mask & __GFP_NORETRY)) {
/*
* If allocating entire pageblock(s) and compaction
* failed because all zones are below low watermarks
@@ -4495,23 +4498,6 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
if (compact_result == COMPACT_SKIPPED ||
compact_result == COMPACT_DEFERRED)
goto nopage;
- }
-
- /*
- * Checks for costly allocations with __GFP_NORETRY, which
- * includes THP page fault allocations
- */
- if (costly_order && (gfp_mask & __GFP_NORETRY)) {
- /*
- * If compaction is deferred for high-order allocations,
- * it is because sync compaction recently failed. If
- * this is the case and the caller requested a THP
- * allocation, we do not want to heavily disrupt the
- * system, so we fail the allocation instead of entering
- * direct reclaim.
- */
- if (compact_result == COMPACT_DEFERRED)
- goto nopage;
/*
* Looks like reclaim/compaction is worth trying, but
--
2.23.0
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