On Sat, Feb 1, 2025 at 1:02 AM Kairui Song <ryncsn@xxxxxxxxx> wrote:
>
> On Thu, Jan 30, 2025 at 6:02 PM Kirill A. Shutemov
> <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> >
> > The recently introduced PG_dropbehind allows for freeing folios
> > immediately after writeback. Unlike PG_reclaim, it does not need vmscan
> > to be involved to get the folio freed.
> >
> > Instead of using folio_set_reclaim(), use folio_set_dropbehind() in
> > pageout().
> >
> > It is safe to leave PG_dropbehind on the folio if, for some reason
> > (bug?), the folio is not in a writeback state after ->writepage().
> > In these cases, the kernel had to clear PG_reclaim as it shared a page
> > flag bit with PG_readahead.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Acked-by: David Hildenbrand <david@xxxxxxxxxx>
> > ---
> > mm/vmscan.c | 9 +++------
> > 1 file changed, 3 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index bc1826020159..c97adb0fdaa4 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -692,19 +692,16 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping,
> > if (shmem_mapping(mapping) && folio_test_large(folio))
> > wbc.list = folio_list;
> >
> > - folio_set_reclaim(folio);
> > + folio_set_dropbehind(folio);
> > +
> > res = mapping->a_ops->writepage(&folio->page, &wbc);
> > if (res < 0)
> > handle_write_error(mapping, folio, res);
> > if (res == AOP_WRITEPAGE_ACTIVATE) {
> > - folio_clear_reclaim(folio);
> > + folio_clear_dropbehind(folio);
> > return PAGE_ACTIVATE;
> > }
> >
> > - if (!folio_test_writeback(folio)) {
> > - /* synchronous write or broken a_ops? */
> > - folio_clear_reclaim(folio);
> > - }
> > trace_mm_vmscan_write_folio(folio);
> > node_stat_add_folio(folio, NR_VMSCAN_WRITE);
> > return PAGE_SUCCESS;
> > --
> > 2.47.2
> >
>
> Hi, I'm seeing following panic with SWAP after this commit:
>
> [ 29.672319] Oops: general protection fault, probably for
> non-canonical address 0xffff88909a3be3: 0000 [#1] PREEMPT SMP NOPTI
> [ 29.675503] CPU: 82 UID: 0 PID: 5145 Comm: tar Kdump: loaded Not
> tainted 6.13.0.ptch-g1fe9ea48ec98 #917
> [ 29.677508] Hardware name: Red Hat KVM/RHEL-AV, BIOS 0.0.0 02/06/2015
> [ 29.678886] RIP: 0010:__lock_acquire+0x20/0x15d0
> [ 29.679891] Code: 90 90 90 90 90 90 90 90 90 90 41 57 41 56 41 55
> 41 54 55 53 48 83 ec 30 8b 2d 10 ac f3 01 44 8b ac 24 88 00 00 00 85
> ed 74 64 <48> 8b 07 49 89 ff 48 3d 20 1d bf 83 74 56 8b 1d 8c f5 b1 01
> 41 89
> [ 29.683852] RSP: 0018:ffffc9000bea3148 EFLAGS: 00010002
> [ 29.684980] RAX: ffff8890874b2940 RBX: 0000000000000200 RCX: 0000000000000000
> [ 29.686510] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00ffff88909a3be3
> [ 29.688031] RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000000
> [ 29.689561] R10: 0000000000000000 R11: 0000000000000020 R12: 00ffff88909a3be3
> [ 29.691087] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> [ 29.692613] FS: 00007fa05c2824c0(0000) GS:ffff88a03fa80000(0000)
> knlGS:0000000000000000
> [ 29.694339] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 29.695581] CR2: 000055f9abb7fc7d CR3: 00000010932f2002 CR4: 0000000000770eb0
> [ 29.697109] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 29.698637] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [ 29.700161] PKRU: 55555554
> [ 29.700759] Call Trace:
> [ 29.701296] <TASK>
> [ 29.701770] ? __die_body+0x1e/0x60
> [ 29.702540] ? die_addr+0x3c/0x60
> [ 29.703267] ? exc_general_protection+0x18f/0x3c0
> [ 29.704290] ? asm_exc_general_protection+0x26/0x30
> [ 29.705345] ? __lock_acquire+0x20/0x15d0
> [ 29.706215] ? lockdep_hardirqs_on_prepare+0xda/0x190
> [ 29.707304] ? asm_sysvec_apic_timer_interrupt+0x1a/0x20
> [ 29.708452] lock_acquire+0xbf/0x2e0
> [ 29.709229] ? folio_unmap_invalidate+0x12f/0x220
> [ 29.710257] ? __folio_end_writeback+0x15d/0x430
> [ 29.711260] ? __folio_end_writeback+0x116/0x430
> [ 29.712261] _raw_spin_lock+0x30/0x40
> [ 29.713064] ? folio_unmap_invalidate+0x12f/0x220
> [ 29.714076] folio_unmap_invalidate+0x12f/0x220
> [ 29.715058] folio_end_writeback+0xdf/0x190
> [ 29.715967] swap_writepage_bdev_sync+0x1e0/0x450
> [ 29.716994] ? __pfx_submit_bio_wait_endio+0x10/0x10
> [ 29.718074] swap_writepage+0x46b/0x6b0
> [ 29.718917] pageout+0x14b/0x360
> [ 29.719628] shrink_folio_list+0x67d/0xec0
> [ 29.720519] ? mark_held_locks+0x48/0x80
> [ 29.721375] evict_folios+0x2a7/0x9e0
> [ 29.722179] try_to_shrink_lruvec+0x19a/0x270
> [ 29.723130] lru_gen_shrink_lruvec+0x70/0xc0
> [ 29.724060] ? __lock_acquire+0x558/0x15d0
> [ 29.724954] shrink_lruvec+0x57/0x780
> [ 29.725754] ? find_held_lock+0x2d/0xa0
> [ 29.726588] ? rcu_read_unlock+0x17/0x60
> [ 29.727449] shrink_node+0x2ad/0x930
> [ 29.728229] do_try_to_free_pages+0xbd/0x4e0
> [ 29.729160] try_to_free_mem_cgroup_pages+0x123/0x2c0
> [ 29.730252] try_charge_memcg+0x222/0x660
> [ 29.731128] charge_memcg+0x3c/0x80
> [ 29.731888] __mem_cgroup_charge+0x30/0x70
> [ 29.732776] shmem_alloc_and_add_folio+0x1a5/0x480
> [ 29.733818] ? filemap_get_entry+0x155/0x390
> [ 29.734748] shmem_get_folio_gfp+0x28c/0x6c0
> [ 29.735680] shmem_write_begin+0x5a/0xc0
> [ 29.736535] generic_perform_write+0x12a/0x2e0
> [ 29.737503] shmem_file_write_iter+0x86/0x90
> [ 29.738428] vfs_write+0x364/0x530
> [ 29.739180] ksys_write+0x6c/0xe0
> [ 29.739906] do_syscall_64+0x66/0x140
> [ 29.740713] entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [ 29.741800] RIP: 0033:0x7fa05c439984
> [ 29.742584] Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f
> 84 00 00 00 00 00 f3 0f 1e fa 80 3d c5 06 0e 00 00 74 13 b8 01 00 00
> 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 55 48 89 e5 48 83 ec 20
> 48 89
> [ 29.746542] RSP: 002b:00007ffece7720f8 EFLAGS: 00000202 ORIG_RAX:
> 0000000000000001
> [ 29.748157] RAX: ffffffffffffffda RBX: 0000000000002800 RCX: 00007fa05c439984
> [ 29.749682] RDX: 0000000000002800 RSI: 000055f9cfa08000 RDI: 0000000000000004
> [ 29.751216] RBP: 00007ffece772140 R08: 0000000000002800 R09: 0000000000000007
> [ 29.752743] R10: 0000000000000180 R11: 0000000000000202 R12: 000055f9cfa08000
> [ 29.754262] R13: 0000000000000004 R14: 0000000000002800 R15: 00000000000009af
> [ 29.755797] </TASK>
> [ 29.756285] Modules linked in: zram virtiofs
>
> I'm testing with PROVE_LOCKING on. It seems folio_unmap_invalidate is
> called for swapcache folio and it doesn't work well, following PATCH
> on top of mm-unstable seems fix it well:
I think there is a bigger problem here. folio_end_reclaim_write()
currently calls folio_unmap_invalidate() to remove the mapping, and
that's very different from what __remove_mapping() does in the reclaim
path: not only it breaks the swapcache case, the shadow entry is also
lost.
