Re: [PATCH mm-unstable v5 01/10] mm: add folio dtor and order setter functions

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On 07.12.22 05:11, Muchun Song wrote:


On Dec 7, 2022, at 11:42, Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:

On 12/07/22 11:34, Muchun Song wrote:


On Nov 30, 2022, at 06:50, Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx> wrote:

Add folio equivalents for set_compound_order() and set_compound_page_dtor().

Also remove extra new-lines introduced by mm/hugetlb: convert
move_hugetlb_state() to folios and mm/hugetlb_cgroup: convert
hugetlb_cgroup_uncharge_page() to folios.

Suggested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Suggested-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
---
include/linux/mm.h | 16 ++++++++++++++++
mm/hugetlb.c       |  4 +---
2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a48c5ad16a5e..2bdef8a5298a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -972,6 +972,13 @@ static inline void set_compound_page_dtor(struct page *page,
page[1].compound_dtor = compound_dtor;
}

+static inline void folio_set_compound_dtor(struct folio *folio,
+ enum compound_dtor_id compound_dtor)
+{
+ VM_BUG_ON_FOLIO(compound_dtor >= NR_COMPOUND_DTORS, folio);
+ folio->_folio_dtor = compound_dtor;
+}
+
void destroy_large_folio(struct folio *folio);

static inline int head_compound_pincount(struct page *head)
@@ -987,6 +994,15 @@ static inline void set_compound_order(struct page *page, unsigned int order)
#endif
}

+static inline void folio_set_compound_order(struct folio *folio,
+ unsigned int order)
+{
+ folio->_folio_order = order;
+#ifdef CONFIG_64BIT
+ folio->_folio_nr_pages = order ? 1U << order : 0;

It seems that you think the user could pass 0 to order. However,
->_folio_nr_pages and ->_folio_order fields are invalid for order-0 pages.
You should not touch it. So this should be:

static inline void folio_set_compound_order(struct folio *folio,
     unsigned int order)
{
	if (!folio_test_large(folio))
		return;

	folio->_folio_order = order;
#ifdef CONFIG_64BIT
	folio->_folio_nr_pages = 1U << order;
#endif
}

I believe this was changed to accommodate the code in
__destroy_compound_gigantic_page().  It is used in a subsequent patch.
Here is the v6.0 version of the routine.

Thanks for your clarification.


static void __destroy_compound_gigantic_page(struct page *page,
unsigned int order, bool demote)
{
	int i;
	int nr_pages = 1 << order;
	struct page *p = page + 1;

	atomic_set(compound_mapcount_ptr(page), 0);
	atomic_set(compound_pincount_ptr(page), 0);

	for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
		p->mapping = NULL;
		clear_compound_head(p);
		if (!demote)
			set_page_refcounted(p);
	}

	set_compound_order(page, 0);
#ifdef CONFIG_64BIT
	page[1].compound_nr = 0;
#endif
	__ClearPageHead(page);
}


Might have been better to change this set_compound_order call to
folio_set_compound_order in this patch.


Agree. It has confused me a lot. I suggest changing the code to the
followings. The folio_test_large() check is still to avoid unexpected
users for OOB.

static inline void folio_set_compound_order(struct folio *folio,
					    unsigned int order)
{
	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
	// or
	// if (!folio_test_large(folio))
	// 	return;

	folio->_folio_order = order;
#ifdef CONFIG_64BIT
	folio->_folio_nr_pages = order ? 1U << order : 0;
#endif
}

Thanks.

On mm-stable, dynamically allocating gigantic pages gives me:

[   23.625105] page:00000000ae27bd2a refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1800
[   23.635117] flags: 0x17fffc00000000(node=0|zone=2|lastcpupid=0x1ffff)
[   23.641969] raw: 0017fffc00000000 ffffa4edc489bb58 fffff784c6000048 0000000000000000
[   23.650141] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
[   23.657907] page dumped because: VM_BUG_ON_FOLIO(!folio_test_large(folio))
[   23.663955] ------------[ cut here ]------------
[   23.667680] kernel BUG at include/linux/mm.h:1030!
[   23.673378] invalid opcode: 0000 [#1] PREEMPT SMP PTI
[   23.681610] CPU: 3 PID: 1220 Comm: bash Not tainted 6.1.0-rc4+ #13
[   23.690281] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.0-1.fc36 04/01/2014
[   23.699837] RIP: 0010:__prep_compound_gigantic_folio+0x115/0x120
[   23.706587] Code: c7 44 24 5c 00 00 00 00 5b 44 89 d0 5d 41 5c 41 5d 41 5e c3 cc cc cc cc 48 83 e8 09
[   23.725954] RSP: 0018:ffffa4edc489bc90 EFLAGS: 00010296
[   23.731001] RAX: 000000000000003e RBX: ffffffffae39a720 RCX: 0000000000000000
[   23.736065] RDX: 0000000000000001 RSI: ffffffffad522c25 RDI: 00000000ffffffff
[   23.740866] RBP: 0000000000040000 R08: 0000000000000000 R09: ffffa4edc489bb58
[   23.745385] R10: 0000000000000003 R11: ffff926d7ff4b028 R12: fffff784c6000000
[   23.749464] R13: 0000000000040000 R14: fffff784c6000000 R15: ffff9266039fb900
[   23.753176] FS:  00007f69a9703740(0000) GS:ffff92696f8c0000(0000) knlGS:0000000000000000
[   23.758299] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   23.761275] CR2: 0000556789080640 CR3: 0000000105568005 CR4: 0000000000770ee0
[   23.764929] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   23.768572] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   23.772221] PKRU: 55555554
[   23.773696] Call Trace:
[   23.776170]  <TASK>
[   23.777258]  alloc_fresh_hugetlb_folio+0x14b/0x220
[   23.779406]  alloc_pool_huge_page+0x7c/0x110
[   23.781273]  __nr_hugepages_store_common+0x191/0x400
[   23.783369]  ? __mod_memcg_lruvec_state+0x93/0x110
[   23.785343]  ? __mod_lruvec_page_state+0xa6/0x1a0
[   23.787223]  ? _copy_from_iter+0x8c/0x540
[   23.788788]  ? __kmem_cache_alloc_node+0x13b/0x2a0
[   23.790577]  ? kernfs_fop_write_iter+0x174/0x1f0
[   23.792313]  nr_hugepages_store+0x57/0x70
[   23.793754]  kernfs_fop_write_iter+0x11b/0x1f0
[   23.795337]  vfs_write+0x1e1/0x3a0
[   23.796531]  ksys_write+0x53/0xd0
[   23.797690]  do_syscall_64+0x37/0x90
[   23.798947]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
[   23.800602] RIP: 0033:0x7f69a9501977
[   23.801798] Code: 0f 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 14
[   23.807322] RSP: 002b:00007ffce87f3338 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[   23.809460] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007f69a9501977
[   23.811485] RDX: 0000000000000002 RSI: 00005652a970e5e0 RDI: 0000000000000001
[   23.813443] RBP: 00005652a970e5e0 R08: 0000000000000000 R09: 0000000000000073
[   23.815385] R10: 0000000000001000 R11: 0000000000000246 R12: 0000000000000002
[   23.817289] R13: 00007f69a95f9780 R14: 0000000000000002 R15: 00007f69a95f49e0
[   23.819176]  </TASK>
[   23.819792] Modules linked in: intel_rapl_msr intel_rapl_common intel_uncore_frequency_common isst_ir
[   23.829056] ---[ end trace 0000000000000000 ]---
[   23.830413] RIP: 0010:__prep_compound_gigantic_folio+0x115/0x120
[   23.832390] Code: c7 44 24 5c 00 00 00 00 5b 44 89 d0 5d 41 5c 41 5d 41 5e c3 cc cc cc cc 48 83 e8 09
[   23.836787] RSP: 0018:ffffa4edc489bc90 EFLAGS: 00010296
[   23.838083] RAX: 000000000000003e RBX: ffffffffae39a720 RCX: 0000000000000000
[   23.839764] RDX: 0000000000000001 RSI: ffffffffad522c25 RDI: 00000000ffffffff
[   23.841456] RBP: 0000000000040000 R08: 0000000000000000 R09: ffffa4edc489bb58
[   23.843150] R10: 0000000000000003 R11: ffff926d7ff4b028 R12: fffff784c6000000
[   23.844836] R13: 0000000000040000 R14: fffff784c6000000 R15: ffff9266039fb900
[   23.846521] FS:  00007f69a9703740(0000) GS:ffff92696f8c0000(0000) knlGS:0000000000000000
[   23.848417] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   23.849797] CR2: 0000556789080640 CR3: 0000000105568005 CR4: 0000000000770ee0
[   23.851491] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   23.853181] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   23.854861] PKRU: 55555554


Something's broken.

--
Thanks,

David / dhildenb





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