The patch titled
Subject: mm/page_alloc: sort out the alloc_contig_range() gfp flags mess
has been added to the -mm mm-unstable branch. Its filename is
mm-page_alloc-sort-out-the-alloc_contig_range-gfp-flags-mess.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-sort-out-the-alloc_contig_range-gfp-flags-mess.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/page_alloc: sort out the alloc_contig_range() gfp flags mess
Date: Tue, 3 Dec 2024 10:47:30 +0100
It's all a bit complicated for alloc_contig_range(). For example, we
don't support many flags, so let's start bailing out on unsupported ones
-- ignoring the placement hints, as we are already given the range to
allocate.
While we currently set cc.gfp_mask, in __alloc_contig_migrate_range() we
simply create yet another GFP mask whereby we ignore the reclaim flags
specify by the caller. That looks very inconsistent.
Let's clean it up, constructing the gfp flags used for
compaction/migration exactly once. Update the documentation of the
gfp_mask parameter for alloc_contig_range() and alloc_contig_pages().
Link: https://lkml.kernel.org/r/20241203094732.200195-5-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Zi Yan <ziy@xxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Madhavan Srinivasan <maddy@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Naveen N Rao <naveen@xxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 48 ++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 44 insertions(+), 4 deletions(-)
--- a/mm/page_alloc.c~mm-page_alloc-sort-out-the-alloc_contig_range-gfp-flags-mess
+++ a/mm/page_alloc.c
@@ -6288,7 +6288,7 @@ static int __alloc_contig_migrate_range(
int ret = 0;
struct migration_target_control mtc = {
.nid = zone_to_nid(cc->zone),
- .gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
+ .gfp_mask = cc->gfp_mask,
.reason = MR_CONTIG_RANGE,
};
struct page *page;
@@ -6384,6 +6384,39 @@ static void split_free_pages(struct list
}
}
+static int __alloc_contig_verify_gfp_mask(gfp_t gfp_mask, gfp_t *gfp_cc_mask)
+{
+ const gfp_t reclaim_mask = __GFP_IO | __GFP_FS | __GFP_RECLAIM;
+ const gfp_t action_mask = __GFP_COMP | __GFP_RETRY_MAYFAIL | __GFP_NOWARN;
+ const gfp_t cc_action_mask = __GFP_RETRY_MAYFAIL | __GFP_NOWARN;
+
+ /*
+ * We are given the range to allocate; node, mobility and placement
+ * hints are irrelevant at this point. We'll simply ignore them.
+ */
+ gfp_mask &= ~(GFP_ZONEMASK | __GFP_RECLAIMABLE | __GFP_WRITE |
+ __GFP_HARDWALL | __GFP_THISNODE | __GFP_MOVABLE);
+
+ /*
+ * We only support most reclaim flags (but not NOFAIL/NORETRY), and
+ * selected action flags.
+ */
+ if (gfp_mask & ~(reclaim_mask | action_mask))
+ return -EINVAL;
+
+ /*
+ * Flags to control page compaction/migration/reclaim, to free up our
+ * page range. Migratable pages are movable, __GFP_MOVABLE is implied
+ * for them.
+ *
+ * Traditionally we always had __GFP_HARDWALL|__GFP_RETRY_MAYFAIL set,
+ * keep doing that to not degrade callers.
+ */
+ *gfp_cc_mask = (gfp_mask & (reclaim_mask | cc_action_mask)) |
+ __GFP_HARDWALL | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL;
+ return 0;
+}
+
/**
* alloc_contig_range() -- tries to allocate given range of pages
* @start: start PFN to allocate
@@ -6392,7 +6425,9 @@ static void split_free_pages(struct list
* #MIGRATE_MOVABLE or #MIGRATE_CMA). All pageblocks
* in range must have the same migratetype and it must
* be either of the two.
- * @gfp_mask: GFP mask to use during compaction
+ * @gfp_mask: GFP mask. Node/zone/placement hints are ignored; only some
+ * action and reclaim modifiers are supported. Reclaim modifiers
+ * control allocation behavior during compaction/migration/reclaim.
*
* The PFN range does not have to be pageblock aligned. The PFN range must
* belong to a single zone.
@@ -6418,11 +6453,14 @@ int alloc_contig_range_noprof(unsigned l
.mode = MIGRATE_SYNC,
.ignore_skip_hint = true,
.no_set_skip_hint = true,
- .gfp_mask = current_gfp_context(gfp_mask),
.alloc_contig = true,
};
INIT_LIST_HEAD(&cc.migratepages);
+ gfp_mask = current_gfp_context(gfp_mask);
+ if (__alloc_contig_verify_gfp_mask(gfp_mask, (gfp_t *)&cc.gfp_mask))
+ return -EINVAL;
+
/*
* What we do here is we mark all pageblocks in range as
* MIGRATE_ISOLATE. Because pageblock and max order pages may
@@ -6565,7 +6603,9 @@ static bool zone_spans_last_pfn(const st
/**
* alloc_contig_pages() -- tries to find and allocate contiguous range of pages
* @nr_pages: Number of contiguous pages to allocate
- * @gfp_mask: GFP mask to limit search and used during compaction
+ * @gfp_mask: GFP mask. Node/zone/placement hints limit the search; only some
+ * action and reclaim modifiers are supported. Reclaim modifiers
+ * control allocation behavior during compaction/migration/reclaim.
* @nid: Target node
* @nodemask: Mask for other possible nodes
*
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-mempolicy-fix-migrate_to_node-assuming-there-is-at-least-one-vma-in-a-mm.patch
mm-filemap-dont-call-folio_test_locked-without-a-reference-in-next_uptodate_folio.patch
docs-tmpfs-update-the-large-folios-policy-for-tmpfs-and-shmem.patch
mm-memory_hotplug-move-debug_pagealloc_map_pages-into-online_pages_range.patch
mm-page_isolation-dont-pass-gfp-flags-to-isolate_single_pageblock.patch
mm-page_isolation-dont-pass-gfp-flags-to-start_isolate_page_range.patch
mm-page_alloc-make-__alloc_contig_migrate_range-static.patch
mm-page_alloc-sort-out-the-alloc_contig_range-gfp-flags-mess.patch
mm-page_alloc-forward-the-gfp-flags-from-alloc_contig_range-to-post_alloc_hook.patch
powernv-memtrace-use-__gfp_zero-with-alloc_contig_pages.patch
