Messages in this thread | | | Subject | Re: ubifs: fix page_count in ->ubifs_migrate_page() | From | zhangjun <> | Date | Thu, 13 Dec 2018 23:14:37 +0800 |
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On 2018/12/13 下午10:23, Richard Weinberger wrote: > Hello zhangjun, > > thanks a lot for bringing this up! > > Am Mittwoch, 12. Dezember 2018, 15:13:57 CET schrieb zhangjun: >> Because the PagePrivate() in UBIFS is different meanings, >> alloc_cma() will fail when one dirty page cache located in >> the type of MIGRATE_CMA >> >> If not adjust the 'extra_count' for dirty page, >> ubifs_migrate_page() -> migrate_page_move_mapping() will >> always return -EAGAIN for: >> expected_count += page_has_private(page) >> This causes the migration to fail until the page cache is cleaned >> >> In general, PagePrivate() indicates that buff_head is already bound >> to this page, and at the same time page_count() will also increase. >> But UBIFS set private flag when the cache is dirty, and page_count() >> not increase. >> Therefore, the expected_count of UBIFS is different from the general >> case. > As you noted, UBIFS uses PG_private a little different. > It uses it as marker and when set, the page counter is not incremented, > since no private data is attached. > The migration code assumes that PG_private indicates a counter of +1. > So, we have to pass a extra count of -1 to migrate_page_move_mapping() if > the flag is set. > Just like F2FS does. Not really nice but hey... > >> Signed-off-by: zhangjun <openzhangj@gmail.com> > Fixes: 4ac1c17b2044 ("UBIFS: Implement ->migratepage()") > >> --- >> fs/ubifs/file.c | 9 ++++++++- >> 1 file changed, 8 insertions(+), 1 deletion(-) >> >> diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c >> index 1b78f2e..2136a5c 100644 >> --- a/fs/ubifs/file.c >> +++ b/fs/ubifs/file.c >> @@ -1480,8 +1480,15 @@ static int ubifs_migrate_page(struct address_space *mapping, >> struct page *newpage, struct page *page, enum migrate_mode mode) >> { >> int rc; >> + int extra_count; >> >> - rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0); >> + /* >> + * UBIFS is using PagePrivate() which can have different meanings across >> + * filesystems. So here adjusting the 'extra_count' make it work. >> + */ > Please rewrite that comment. > /* > * UBIFS uses PG_private as marker and does not raise the page counter. > * migrate_page_move_mapping() expects a incremented counter if PG_private > * is set. Therefore pass -1 as extra_count for this case. > */ > >> + extra_count = 0 - page_has_private(page); > if (page_has_private(page)) > extra_count = -1; > > That way this corner is much more obvious. > > Thanks, > //richard > > Hello Richard.
Thank you very much for your help.
1. Can i use your description for comment? like this:
/* * UBIFS uses PG_private a little different. * It uses it as marker and when set, the page counter is not incremented, * since no private data is attached. * The migration code assumes that PG_private indicates a counter of +1. * So, we have to pass a extra count of -1 to migrate_page_move_mapping() if * the flag is set. */
2. It's more obvious, but the branch may break the cpu pipeline?
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