在 2020/8/13 下午12:02, Alexander Duyck 写道: > From: Alexander Duyck <[email protected]> > > The only user of test_and_set_skip was isolate_migratepages_block and it > was using it after a call that was testing and clearing the LRU flag. As > such it really didn't need to be behind the LRU lock anymore as it wasn't > really fulfilling its purpose. > > With that being the case we can simply drop the bit and instead directly > just call the set_pageblock_skip function if the page we are working on is > the valid_page at the start of the pageblock. It shouldn't be possible for > us to encounter the bit being set since we obtained the LRU flag for the > first page in the pageblock which means we would have exclusive access to > setting the skip bit. As such we don't need to worry about the abort case > since no other thread will be able to call what used to be > test_and_set_skip. > > Since we have dropped the late abort case we can drop the code that was > clearing the LRU flag and calling page_put since the abort case will now > not be holding a reference to a page. > > Signed-off-by: Alexander Duyck <[email protected]> After my false sharing remove on pageblock_flags, this patch looks fine with a minor change > --- > mm/compaction.c | 50 +++++++------------------------------------------- > 1 file changed, 7 insertions(+), 43 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 5021a18ef722..c1e9918f9dd4 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -399,29 +399,6 @@ void reset_isolation_suitable(pg_data_t *pgdat) > } > } > > -/* > - * Sets the pageblock skip bit if it was clear. Note that this is a hint as > - * locks are not required for read/writers. Returns true if it was already > set. > - */ > -static bool test_and_set_skip(struct compact_control *cc, struct page *page, > - unsigned long pfn) > -{ > - bool skip; > - > - /* Do no update if skip hint is being ignored */ > - if (cc->ignore_skip_hint) > - return false; > - > - if (!IS_ALIGNED(pfn, pageblock_nr_pages)) > - return false; > - > - skip = get_pageblock_skip(page); > - if (!skip && !cc->no_set_skip_hint) > - skip = !set_pageblock_skip(page); > - > - return skip; > -} > - > static void update_cached_migrate(struct compact_control *cc, unsigned long > pfn) > { > struct zone *zone = cc->zone; > @@ -480,12 +457,6 @@ static inline void update_pageblock_skip(struct > compact_control *cc, > static void update_cached_migrate(struct compact_control *cc, unsigned long > pfn) > { > } > - > -static bool test_and_set_skip(struct compact_control *cc, struct page *page, > - unsigned long pfn) > -{ > - return false; > -} > #endif /* CONFIG_COMPACTION */ > > /* > @@ -895,7 +866,6 @@ static bool too_many_isolated(pg_data_t *pgdat) > if (!valid_page && IS_ALIGNED(low_pfn, pageblock_nr_pages)) { > if (!cc->ignore_skip_hint && get_pageblock_skip(page)) { > low_pfn = end_pfn; > - page = NULL; > goto isolate_abort; > } > valid_page = page; > @@ -991,6 +961,13 @@ static bool too_many_isolated(pg_data_t *pgdat) > if (!TestClearPageLRU(page)) > goto isolate_fail_put; > > + /* Indicate that we want exclusive access to this pageblock */ > + if (page == valid_page) { > + skip_updated = true; > + if (!cc->ignore_skip_hint) if (!cc->ignore_skip_hint && !cc->no_set_skip_hint) no_set_skip_hint needs to add here. Thanks Alex > + set_pageblock_skip(page); > + } > + > /* If we already hold the lock, we can skip some rechecking */ > if (!lruvec || !lruvec_holds_page_lru_lock(page, lruvec)) { > if (lruvec) > @@ -1002,13 +979,6 @@ static bool too_many_isolated(pg_data_t *pgdat) > > lruvec_memcg_debug(lruvec, page); > > - /* Try get exclusive access under lock */ > - if (!skip_updated) { > - skip_updated = true; > - if (test_and_set_skip(cc, page, low_pfn)) > - goto isolate_abort; > - } > - > /* > * Page become compound since the non-locked check, > * and it's on LRU. It can only be a THP so the order > @@ -1094,15 +1064,9 @@ static bool too_many_isolated(pg_data_t *pgdat) > if (unlikely(low_pfn > end_pfn)) > low_pfn = end_pfn; > > - page = NULL; > - > isolate_abort: > if (lruvec) > unlock_page_lruvec_irqrestore(lruvec, flags); > - if (page) { > - SetPageLRU(page); > - put_page(page); > - } > > /* > * Updated the cached scanner pfn once the pageblock has been scanned >
