Re: [PATCHv3 06/11] mm/vmscan: Use PG_dropbehind instead of PG_reclaim
From: Shakeel Butt <shakeel.butt@linux.dev>
Date: 2025-01-31 21:33:17
Also in:
dri-devel, intel-gfx, linux-fsdevel, linux-mm, lkml
On Thu, Jan 30, 2025 at 12:00:44PM +0200, Kirill A. Shutemov 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.
Is it correct to say that leaving PG_dropbehind on folios which doesn't have writeback state after ->writepage() (i.e. store to zswap) is fine because PG_dropbehind is not in PAGE_FLAGS_CHECK_AT_FREE?
quoted hunk ↗ jump to hunk
Signed-off-by: Kirill A. Shutemov <redacted> Acked-by: David Hildenbrand <redacted> --- 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