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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rdCdn-000000049c5-06P8; Thu, 22 Feb 2024 17:13:47 +0000 Date: Thu, 22 Feb 2024 17:13:46 +0000 From: Matthew Wilcox To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton Subject: Re: [PATCH v1] mm: remove total_mapcount() Message-ID: References: <20240222160943.622386-1-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240222160943.622386-1-david@redhat.com> X-Rspamd-Queue-Id: 5849CC0007 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 88xwyayfq65dnukdzsaz3c8zmyatzx84 X-HE-Tag: 1708622029-199880 X-HE-Meta: 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 nz/CiP8i FmJ1yHT28smgjyaGGRz5oFf7gIE5ltqiW4v7BzPfJHeQ4POgSLwEmo21hK6yNRZQMmc1hzgRHKWoCgSCYu2NY5E/w52NGwLT3w/9zh4sUONYkLBkBZSjUj8cTgQPpTV+SCClL+VMhWKs1NDOZMoYNvsCumNo9ol3VORD2iyAQFECFTYUPRiCNPeDRx84/OtSu/aAw/D1rnRCOBYmh1iM+aaVIsOGkkd3QktnGi8iTAl3FnJ/aAcNXl948kg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Feb 22, 2024 at 05:09:43PM +0100, David Hildenbrand wrote: > We always get a head page, so we can just naturally interpret is as a folio > (similar to other code). memfd seems rather confused about how to iterate over the page cache. Perhaps we could sort that out and then delete total_mapcount as a second patch? I haven't tested this at all, but ... Signed-off-by: Matthew Wilcox (Oracle) diff --git a/mm/memfd.c b/mm/memfd.c index d3a1ba4208c9..45e55b0e3cbe 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -29,28 +29,29 @@ #define MEMFD_TAG_PINNED PAGECACHE_TAG_TOWRITE #define LAST_SCAN 4 /* about 150ms max */ +static bool memfd_extra_refs(struct folio *folio) +{ + return folio_ref_count(folio) - folio_mapcount(folio) != + folio_nr_pages(folio); +} + static void memfd_tag_pins(struct xa_state *xas) { - struct page *page; + struct folio *folio; int latency = 0; - int cache_count; lru_add_drain(); xas_lock_irq(xas); - xas_for_each(xas, page, ULONG_MAX) { - cache_count = 1; - if (!xa_is_value(page) && - PageTransHuge(page) && !PageHuge(page)) - cache_count = HPAGE_PMD_NR; - - if (!xa_is_value(page) && - page_count(page) - total_mapcount(page) != cache_count) + xas_for_each(xas, folio, ULONG_MAX) { + /* Can we have shadow/swap entries in memfd? */ + if (xa_is_value(folio)) + continue; + + if (memfd_extra_refs(folio)) xas_set_mark(xas, MEMFD_TAG_PINNED); - if (cache_count != 1) - xas_set(xas, page->index + cache_count); - latency += cache_count; + latency++; if (latency < XA_CHECK_SCHED) continue; latency = 0; @@ -75,7 +76,6 @@ static void memfd_tag_pins(struct xa_state *xas) static int memfd_wait_for_pins(struct address_space *mapping) { XA_STATE(xas, &mapping->i_pages, 0); - struct page *page; int error, scan; memfd_tag_pins(&xas); @@ -83,7 +83,7 @@ static int memfd_wait_for_pins(struct address_space *mapping) error = 0; for (scan = 0; scan <= LAST_SCAN; scan++) { int latency = 0; - int cache_count; + struct folio *folio; if (!xas_marked(&xas, MEMFD_TAG_PINNED)) break; @@ -95,16 +95,10 @@ static int memfd_wait_for_pins(struct address_space *mapping) xas_set(&xas, 0); xas_lock_irq(&xas); - xas_for_each_marked(&xas, page, ULONG_MAX, MEMFD_TAG_PINNED) { + xas_for_each_marked(&xas, folio, ULONG_MAX, MEMFD_TAG_PINNED) { bool clear = true; - cache_count = 1; - if (!xa_is_value(page) && - PageTransHuge(page) && !PageHuge(page)) - cache_count = HPAGE_PMD_NR; - - if (!xa_is_value(page) && cache_count != - page_count(page) - total_mapcount(page)) { + if (memfd_extra_refs(folio)) { /* * On the last scan, we clean up all those tags * we inserted; but make a note that we still @@ -118,8 +112,7 @@ static int memfd_wait_for_pins(struct address_space *mapping) if (clear) xas_clear_mark(&xas, MEMFD_TAG_PINNED); - latency += cache_count; - if (latency < XA_CHECK_SCHED) + if (++latency < XA_CHECK_SCHED) continue; latency = 0;