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Mon, 26 Feb 2024 14:13:27 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, David Hildenbrand , Andrew Morton , Matthew Wilcox Subject: [PATCH v2 1/2] mm/memfd: refactor memfd_tag_pins() and memfd_wait_for_pins() Date: Mon, 26 Feb 2024 15:13:23 +0100 Message-ID: <20240226141324.278526-2-david@redhat.com> In-Reply-To: <20240226141324.278526-1-david@redhat.com> References: <20240226141324.278526-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 1988C4001E X-Stat-Signature: jc5p59g75nox8frrbk5hbjnutc858z4d X-Rspam-User: X-HE-Tag: 1708956848-684787 X-HE-Meta: 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 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: Both functions are the remaining users of total_mapcount(). Let's get rid of the calls by converting the code to folios. As it turns out, the code is unnecessarily complicated, especially: 1) We can query the number of pagecache references for a folio simply via folio_nr_pages(). This will handle other folio sizes in the future correctly. 2) The xas_set(xas, page->index + cache_count) call to increment the iterator for large folios is not required. Remove it. Further, simplify the XA_CHECK_SCHED check, counting each entry exactly once. Memfd pages can be swapped out when using shmem; leave xa_is_value() checks in place. Co-developed-by: Matthew Wilcox (Oracle) Signed-off-by: Matthew Wilcox (Oracle) Signed-off-by: David Hildenbrand Reviewed-by: Matthew Wilcox (Oracle) --- mm/memfd.c | 47 ++++++++++++++++++----------------------------- 1 file changed, 18 insertions(+), 29 deletions(-) diff --git a/mm/memfd.c b/mm/memfd.c index d3a1ba4208c90..7d8d3ab3fa378 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -29,29 +29,25 @@ #define MEMFD_TAG_PINNED PAGECACHE_TAG_TOWRITE #define LAST_SCAN 4 /* about 150ms max */ +static bool memfd_folio_has_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) { + if (!xa_is_value(folio) && memfd_folio_has_extra_refs(folio)) xas_set_mark(xas, MEMFD_TAG_PINNED); - if (cache_count != 1) - xas_set(xas, page->index + cache_count); - latency += cache_count; - if (latency < XA_CHECK_SCHED) + if (++latency < XA_CHECK_SCHED) continue; latency = 0; @@ -66,16 +62,16 @@ static void memfd_tag_pins(struct xa_state *xas) /* * Setting SEAL_WRITE requires us to verify there's no pending writer. However, * via get_user_pages(), drivers might have some pending I/O without any active - * user-space mappings (eg., direct-IO, AIO). Therefore, we look at all pages + * user-space mappings (eg., direct-IO, AIO). Therefore, we look at all folios * and see whether it has an elevated ref-count. If so, we tag them and wait for * them to be dropped. * The caller must guarantee that no new user will acquire writable references - * to those pages to avoid races. + * to those folios to avoid races. */ static int memfd_wait_for_pins(struct address_space *mapping) { XA_STATE(xas, &mapping->i_pages, 0); - struct page *page; + struct folio *folio; int error, scan; memfd_tag_pins(&xas); @@ -83,7 +79,6 @@ 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; if (!xas_marked(&xas, MEMFD_TAG_PINNED)) break; @@ -95,20 +90,15 @@ 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 (!xa_is_value(folio) && + memfd_folio_has_extra_refs(folio)) { /* * On the last scan, we clean up all those tags * we inserted; but make a note that we still - * found pages pinned. + * found folios pinned. */ if (scan == LAST_SCAN) error = -EBUSY; @@ -118,8 +108,7 @@ 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;