On Wed, Aug 28, 2024 at 08:36:03PM +0800, Kefeng Wang wrote: > > > On 2024/8/28 18:04, Baolin Wang wrote: > > Hi Kefeng, > > > > On 2024/8/26 12:01, Kefeng Wang wrote: > > > The tail page will always fail to isolate for non-lru-movable and > > > LRU page in isolate_migratepages_block(), so move PageTail check > > > ahead, then convert to use folio_isolate_movable() helper and more > > > folios. > > > > > > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> > > > --- > > > mm/compaction.c | 32 +++++++++++++++++--------------- > > > 1 file changed, 17 insertions(+), 15 deletions(-) > > > > > > diff --git a/mm/compaction.c b/mm/compaction.c > > > index a2b16b08cbbf..aa2e8bb9fa58 100644 > > > --- a/mm/compaction.c > > > +++ b/mm/compaction.c > > > @@ -1074,39 +1074,41 @@ isolate_migratepages_block(struct > > > compact_control *cc, unsigned long low_pfn, > > > } > > > } > > > + if (PageTail(page)) > > > + goto isolate_fail; > > > + > > > + folio = page_folio(page); > > > > I wonder if this is stable. Before page_folio(), it does not hold a > > reference on the page, so seems we should re-check the folio still > > contains this page after gaining a reference on the folio? > > Oh, you are right, so two way to avoid this, > > 1) re-check 'page_folio(page) == folio', but this need change a little > more. > > 2) directly use folio_get_nontail_page(page) here, and folio_put in the > following path, this will try to get for any pages, but it should be > accepted ? > > I'd prefer 2) but any other suggestion? I think option 2 makes sense, and simply use folio_put() on success and goto isolate_fail_put on failure instead of isolate_fail. With option 2, it might make sense to have folio_isolate_movable() expect to be passed a folio with elevated refcount. Then it could be treated similarly to its sister function folio_isolate_lru() and simply use folio_get() for its reference.
