On 6 Jun 2024, at 2:42, xu.xin16@xxxxxxxxxx wrote: > From: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx> > > When I did a large folios split test, a WARNING > "[ 5059.122759][ T166] Cannot split file folio to non-0 order" > was triggered. But the test cases are only for anonmous folios. > while mapping_large_folio_support() is only reasonable for page > cache folios. > > In split_huge_page_to_list_to_order(), the folio passed to > mapping_large_folio_support() maybe anonmous folio. The > folio_test_anon() check is missing. So the split of the anonmous THP > is failed. This is also the same for shmem_mapping(). We'd better add > a check for both. But the shmem_mapping() in __split_huge_page() is > not involved, as for anonmous folios, the end parameter is set to -1, so > (head[i].index >= end) is always false. shmem_mapping() is not called. > > Also add a VM_WARN_ON_ONCE() in mapping_large_folio_support() > for anon mapping, So we can detect the wrong use more easily. > > THP folios maybe exist in the pagecache even the file system doesn't > support large folio, it is because when CONFIG_TRANSPARENT_HUGEPAGE > is enabled, khugepaged will try to collapse read-only file-backed pages > to THP. But the mapping does not actually support multi order > large folios properly. > > Using /sys/kernel/debug/split_huge_pages to verify this, with this > patch, large anon THP is successfully split and the warning is ceased. > > Signed-off-by: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx> > --- > include/linux/pagemap.h | 4 ++++ > mm/huge_memory.c | 27 ++++++++++++++++----------- > 2 files changed, 20 insertions(+), 11 deletions(-) Reviewed-by: Zi Yan <ziy@xxxxxxxxxx> Thanks. Best Regards, Yan, Zi
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