On 24 Jan 2022, at 13:11, David Rientjes wrote: > On Mon, 24 Jan 2022, Muchun Song wrote: > >> The D-cache maintenance inside move_to_new_page() only consider one page, >> there is still D-cache maintenance issue for tail pages of THP. Fix this >> by not using flush_dcache_folio() since it is not backportable. >> > > The mention of being backportable suggests that we should backport this, > likely to 4.14+. So should it be marked as stable? Hmm, after more digging, I am not sure if the bug exists. For THP migration, flush_cache_range() is used in remove_migration_pmd(). The flush_dcache_page() was added by Lars Persson (cc’d) to solve the data corruption on MIPS[1], but THP migration is only enabled on x86_64, PPC_BOOK3S_64, and ARM64. To make code more consistent, I guess flush_cache_range() in remove_migration_pmd() can be removed, since it is superseded by the flush_dcache_page() below. The Fixes can be dropped. Let me know if I miss anything. > > That aside, should there be a follow-up patch that converts to using > flush_dcache_folio()? Are you suggesting to convert just this code or the entire move_to_new_page() to use folio? The latter might be more desirable, since the code will be more consistent. [1] https://lore.kernel.org/all/20190315083502.11849-1-larper@xxxxxxxx/T/#u > >> Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path") >> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> >> --- >> Changes in v2: >> - Using a for loop instead of the folio variant for backportable. >> >> mm/migrate.c | 7 +++++-- >> 1 file changed, 5 insertions(+), 2 deletions(-) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index c9296d63878d..c418e8d92b9c 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -933,9 +933,12 @@ static int move_to_new_page(struct page *newpage, struct page *page, >> if (!PageMappingFlags(page)) >> page->mapping = NULL; >> >> - if (likely(!is_zone_device_page(newpage))) >> - flush_dcache_page(newpage); >> + if (likely(!is_zone_device_page(newpage))) { >> + int i, nr = compound_nr(newpage); >> >> + for (i = 0; i < nr; i++) >> + flush_dcache_page(newpage + i); >> + } >> } >> out: >> return rc; >> -- >> 2.11.0 >> >> >> -- Best Regards, Yan, Zi
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