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Thu, 29 Aug 2024 16:59:08 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, cgroups@vger.kernel.org, x86@kernel.org, linux-fsdevel@vger.kernel.org, David Hildenbrand , Andrew Morton , "Matthew Wilcox (Oracle)" , Tejun Heo , Zefan Li , Johannes Weiner , =?utf-8?q?Michal_Koutn=C3=BD?= , Jonathan Corbet , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen Subject: [PATCH v1 16/17] fs/proc/task_mmu: remove per-page mapcount dependency for smaps/smaps_rollup (CONFIG_NO_PAGE_MAPCOUNT) Date: Thu, 29 Aug 2024 18:56:19 +0200 Message-ID: <20240829165627.2256514-17-david@redhat.com> In-Reply-To: <20240829165627.2256514-1-david@redhat.com> References: <20240829165627.2256514-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: CC1A7140007 X-Stat-Signature: ao5phq7t1ewnwfd38uwmajwiun8z55dq X-HE-Tag: 1724950762-869223 X-HE-Meta: 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 znTDTdnD rQDALIs3Feh9idmwow4hVXWW4jMsVlvT9Ika0bLBkUq/AffitUhho/wFpUwU4RWuxzW7gJ+LL0MDAsCgniKr/xdLdzhEPB6+vwH+bejY8j7UYZnZsAcipmc/8GPSGeqTDO9G2TuEzEej8pNcJE6vqme67TsSHxINwel8j1GuutJFVoH8AXSBeyPLS14gmal3NTUGrTdFTAmIhymKM6BX00/DTxGgvWDunPTx6Cp6Cxao2sA51E5EWqE/MdL67zMViv0vFkXTEmjKpeAP4HiuiYeFjHdeLCQ/+BvevKEc0RKp/lGEa1OFjhGtKpX8i+yZmMoCB8X36dhY5GQjpFoTE+8Fy7TEn8JDzoXzU2bWpOi4eApuYLVq9k5IWSA== 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List-ID: List-Subscribe: List-Unsubscribe: Let's implement an alternative when per-page mapcounts in large folios are no longer maintained -- soon with CONFIG_NO_PAGE_MAPCOUNT. When computing the output for smaps / smaps_rollups, in particular when calculating the USS (Unique Set Size) and the PSS (Proportional Set Size), we still rely on per-page mapcounts. To determine private vs. shared, we'll use folio_likely_mapped_shared(), similar to how we handle PM_MMAP_EXCLUSIVE. Similarly, we might now under-estimate the USS and count pages towards "shared" that are actually "private" ("exclusively mapped"). When calculating the PSS, we'll now also use the average per-page mapcount for large folios: this can result in both, an over-estimation and an under-estimation of the PSS. The difference is not expected to matter much in practice, but we'll have to learn as we go. We can now provide folio_precise_page_mapcount() only with CONFIG_PAGE_MAPCOUNT, and remove one of the last users of per-page mapcounts when CONFIG_NO_PAGE_MAPCOUNT is enabled. Document the new behavior. Signed-off-by: David Hildenbrand --- Documentation/filesystems/proc.rst | 13 +++++++++++++ fs/proc/internal.h | 2 ++ fs/proc/task_mmu.c | 17 +++++++++++++++-- 3 files changed, 30 insertions(+), 2 deletions(-) diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index bed03e77c0f91..7cbab4135f244 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -504,6 +504,19 @@ Note that even a page which is part of a MAP_SHARED mapping, but has only a single pte mapped, i.e. is currently used by only one process, is accounted as private and not as shared. +Note that in some kernel configurations, all pages part of a larger allocation +(e.g., THP) might be considered "shared" if the large allocation is +considered "shared": if not all pages are exclusive to the same process. +Further, some kernel configurations might consider larger allocations "shared", +if they were at one point considered "shared", even if they would now be +considered "exclusive". + +Some kernel configurations do not track the precise number of times a page part +of a larger allocation is mapped. In this case, when calculating the PSS, the +average number of mappings per page in this larger allocation might be used +as an approximation for the number of mappings of a page. The PSS calculation +will be imprecise in this case. + "Referenced" indicates the amount of memory currently marked as referenced or accessed. diff --git a/fs/proc/internal.h b/fs/proc/internal.h index 3c687f97e18c4..8c9ef19526d2b 100644 --- a/fs/proc/internal.h +++ b/fs/proc/internal.h @@ -143,6 +143,7 @@ unsigned name_to_int(const struct qstr *qstr); /* Worst case buffer size needed for holding an integer. */ #define PROC_NUMBUF 13 +#ifdef CONFIG_PAGE_MAPCOUNT /** * folio_precise_page_mapcount() - Number of mappings of this folio page. * @folio: The folio. @@ -173,6 +174,7 @@ static inline int folio_precise_page_mapcount(struct folio *folio, return mapcount; } +#endif /* CONFIG_PAGE_MAPCOUNT */ /** * folio_average_page_mapcount() - Average number of mappings per page in this diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 3d9fe99346478..30306e231ff04 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -734,6 +734,8 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page, struct folio *folio = page_folio(page); int i, nr = compound ? compound_nr(page) : 1; unsigned long size = nr * PAGE_SIZE; + bool exclusive; + int mapcount; /* * First accumulate quantities that depend only on |size| and the type @@ -774,18 +776,29 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page, dirty, locked, present); return; } + +#ifndef CONFIG_PAGE_MAPCOUNT + mapcount = folio_average_page_mapcount(folio); + exclusive = !folio_likely_mapped_shared(folio); +#endif + /* * We obtain a snapshot of the mapcount. Without holding the folio lock * this snapshot can be slightly wrong as we cannot always read the * mapcount atomically. */ for (i = 0; i < nr; i++, page++) { - int mapcount = folio_precise_page_mapcount(folio, page); unsigned long pss = PAGE_SIZE << PSS_SHIFT; + +#ifdef CONFIG_PAGE_MAPCOUNT + mapcount = folio_precise_page_mapcount(folio, page); + exclusive = mapcount < 2; +#endif + if (mapcount >= 2) pss /= mapcount; smaps_page_accumulate(mss, folio, PAGE_SIZE, pss, - dirty, locked, mapcount < 2); + dirty, locked, exclusive); } }