From nobody Wed Dec 17 15:55:17 2025 Received: from m16.mail.126.com (m16.mail.126.com [220.197.31.9]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 0FBF2522F; Sat, 14 Dec 2024 06:40:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=220.197.31.9 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734158429; cv=none; b=sQ4YD7+surMzH1CR1nimRfff89kKuI+cWeSUYs/bACySUbXHs3Eh0Cg8JjR+pBJXw5Tx0mC21VIbb3xnvQ5JbjyUrdZW8yVCVbGpvI1syrTEJv+S3QRO8xnWGYHniI/5qBndKl5QTAlYmHnx/Jb9VDg2lMxCeX0BUKBbWMiv5tY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734158429; c=relaxed/simple; bh=A0eBcWQArwQLrfg8t0zZ0AtFF5oj0KFDRa6xoPxT6zo=; h=From:To:Cc:Subject:Date:Message-Id; b=bhm0sK4qpAtghMj609sCnMHuujkpUGn7bQwdsaOC08rkRP8VUbUMUE6TDgmxebBzu1L/aa4YsJllM3uTFAibp9OY1G+vQtm43gp37DlaBWcKvZgQ/2MifkzSRPgSu05NzCsSc5ZOZpBD5sAAJ8+4HmyREGVP7LXGJKpU8s27PxE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=126.com; spf=pass smtp.mailfrom=126.com; dkim=pass (1024-bit key) header.d=126.com header.i=@126.com header.b=o7LkcPDa; arc=none smtp.client-ip=220.197.31.9 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=126.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=126.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=126.com header.i=@126.com header.b="o7LkcPDa" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=126.com; s=s110527; h=From:Subject:Date:Message-Id; bh=YLxCN2Gesg12CJxR+/ GXPQjMM9x70eFi/qCoE9PaI/w=; b=o7LkcPDav8oUYppbM2JA0u9rzgI03m9lI2 PJDjHiK9GGCCqqvZbZ5uyFImiE9mAe87GlbSZPKuMTL2J1SETOD5De5RSxcCLTMo O8fE4Xawo6m5ynpxU84X2SFcZGB9pXhWhpF5ReOZ1VgeTzp2q7FQerxIyEcPrNOu 8zpM47SnQ= Received: from hg-OptiPlex-7040.hygon.cn (unknown [118.242.3.34]) by gzsmtp5 (Coremail) with SMTP id qSkvCgDnr_NuJF1n7VZTCQ--.7274S2; Sat, 14 Dec 2024 14:23:43 +0800 (CST) From: yangge1116@126.com To: akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, 21cnbao@gmail.com, david@redhat.com, baolin.wang@linux.alibaba.com, vbabka@suse.cz, liuzixing@hygon.cn, yangge Subject: [PATCH V2] mm, compaction: don't use ALLOC_CMA in long term GUP flow Date: Sat, 14 Dec 2024 14:23:40 +0800 Message-Id: <1734157420-31110-1-git-send-email-yangge1116@126.com> X-Mailer: git-send-email 2.7.4 X-CM-TRANSID: qSkvCgDnr_NuJF1n7VZTCQ--.7274S2 X-Coremail-Antispam: 1Uf129KBjvJXoWxtry8Zr4kJrWUGr4xXr4fKrg_yoWxuF13pF 18ZasFyws5XF13Gr48tF409a15tw4xGF18JryIgw1xZw1akFn2v3WkKFy7AF15XryayF4Y qFWq9ryDGFsxAaDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x0zNLvKwUUUUU= X-CM-SenderInfo: 51dqwwjhrrila6rslhhfrp/1tbifgq1G2ddD3K5DQAAsp Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" From: yangge Since commit 984fdba6a32e ("mm, compaction: use proper alloc_flags in __compaction_suitable()") allow compaction to proceed when free pages required for compaction reside in the CMA pageblocks, it's possible that __compaction_suitable() always returns true, and in some cases, it's not acceptable. There are 4 NUMA nodes on my machine, and each NUMA node has 32GB of memory. I have configured 16GB of CMA memory on each NUMA node, and starting a 32GB virtual machine with device passthrough is extremely slow, taking almost an hour. During the start-up of the virtual machine, it will call pin_user_pages_remote(..., FOLL_LONGTERM, ...) to allocate memory. Long term GUP cannot allocate memory from CMA area, so a maximum of 16 GB of no-CMA memory on a NUMA node can be used as virtual machine memory. Since there is 16G of free CMA memory on the NUMA node, watermark for order-0 always be met for compaction, so __compaction_suitable() always returns true, even if the node is unable to allocate non-CMA memory for the virtual machine. For costly allocations, because __compaction_suitable() always returns true, __alloc_pages_slowpath() can't exit at the appropriate place, resulting in excessively long virtual machine startup times. Call trace: __alloc_pages_slowpath if (compact_result =3D=3D COMPACT_SKIPPED || compact_result =3D=3D COMPACT_DEFERRED) goto nopage; // should exit __alloc_pages_slowpath() from here In order to quickly fall back to remote node, we should remove=20 ALLOC_CMA both in __compaction_suitable() and __isolate_free_page()=20 in long term GUP flow. After this fix, starting a 32GB virtual machine with device passthrough takes only a few seconds. Fixes: 984fdba6a32e ("mm, compaction: use proper alloc_flags in __compactio= n_suitable()") Cc: Signed-off-by: yangge --- V2: - using the 'cc->alloc_flags' to determin if 'ALLOC_CMA' is needed - rich the commit log description include/linux/compaction.h | 3 ++- mm/compaction.c | 18 +++++++++++------- mm/page_alloc.c | 4 +++- mm/vmscan.c | 4 ++-- 4 files changed, 18 insertions(+), 11 deletions(-) diff --git a/include/linux/compaction.h b/include/linux/compaction.h index e947764..0c6f97a 100644 --- a/include/linux/compaction.h +++ b/include/linux/compaction.h @@ -90,7 +90,8 @@ extern enum compact_result try_to_compact_pages(gfp_t gfp= _mask, struct page **page); extern void reset_isolation_suitable(pg_data_t *pgdat); extern bool compaction_suitable(struct zone *zone, int order, - int highest_zoneidx); + int highest_zoneidx, + unsigned int alloc_flags); =20 extern void compaction_defer_reset(struct zone *zone, int order, bool alloc_success); diff --git a/mm/compaction.c b/mm/compaction.c index 07bd227..585f5ab 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -2381,9 +2381,11 @@ static enum compact_result compact_finished(struct c= ompact_control *cc) =20 static bool __compaction_suitable(struct zone *zone, int order, int highest_zoneidx, + unsigned int alloc_flags, unsigned long wmark_target) { unsigned long watermark; + bool use_cma; /* * Watermarks for order-0 must be met for compaction to be able to * isolate free pages for migration targets. This means that the @@ -2395,25 +2397,27 @@ static bool __compaction_suitable(struct zone *zone= , int order, * even if compaction succeeds. * For costly orders, we require low watermark instead of min for * compaction to proceed to increase its chances. - * ALLOC_CMA is used, as pages in CMA pageblocks are considered - * suitable migration targets + * In addition to long term GUP flow, ALLOC_CMA is used, as pages in + * CMA pageblocks are considered suitable migration targets */ watermark =3D (order > PAGE_ALLOC_COSTLY_ORDER) ? low_wmark_pages(zone) : min_wmark_pages(zone); watermark +=3D compact_gap(order); + use_cma =3D !!(alloc_flags & ALLOC_CMA); return __zone_watermark_ok(zone, 0, watermark, highest_zoneidx, - ALLOC_CMA, wmark_target); + use_cma ? ALLOC_CMA : 0, wmark_target); } =20 /* * compaction_suitable: Is this suitable to run compaction on this zone no= w? */ -bool compaction_suitable(struct zone *zone, int order, int highest_zoneidx) +bool compaction_suitable(struct zone *zone, int order, int highest_zoneidx, + unsigned int alloc_flags) { enum compact_result compact_result; bool suitable; =20 - suitable =3D __compaction_suitable(zone, order, highest_zoneidx, + suitable =3D __compaction_suitable(zone, order, highest_zoneidx, alloc_fl= ags, zone_page_state(zone, NR_FREE_PAGES)); /* * fragmentation index determines if allocation failures are due to @@ -2474,7 +2478,7 @@ bool compaction_zonelist_suitable(struct alloc_contex= t *ac, int order, available =3D zone_reclaimable_pages(zone) / order; available +=3D zone_page_state_snapshot(zone, NR_FREE_PAGES); if (__compaction_suitable(zone, order, ac->highest_zoneidx, - available)) + alloc_flags, available)) return true; } =20 @@ -2499,7 +2503,7 @@ compaction_suit_allocation_order(struct zone *zone, u= nsigned int order, alloc_flags)) return COMPACT_SUCCESS; =20 - if (!compaction_suitable(zone, order, highest_zoneidx)) + if (!compaction_suitable(zone, order, highest_zoneidx, alloc_flags)) return COMPACT_SKIPPED; =20 return COMPACT_CONTINUE; diff --git a/mm/page_alloc.c b/mm/page_alloc.c index dde19db..9a5dfda 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2813,6 +2813,7 @@ int __isolate_free_page(struct page *page, unsigned i= nt order) { struct zone *zone =3D page_zone(page); int mt =3D get_pageblock_migratetype(page); + bool pin; =20 if (!is_migrate_isolate(mt)) { unsigned long watermark; @@ -2823,7 +2824,8 @@ int __isolate_free_page(struct page *page, unsigned i= nt order) * exists. */ watermark =3D zone->_watermark[WMARK_MIN] + (1UL << order); - if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA)) + pin =3D !!(current->flags & PF_MEMALLOC_PIN); + if (!zone_watermark_ok(zone, 0, watermark, 0, pin ? 0 : ALLOC_CMA)) return 0; } =20 diff --git a/mm/vmscan.c b/mm/vmscan.c index 5e03a61..806f031 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -5815,7 +5815,7 @@ static inline bool should_continue_reclaim(struct pgl= ist_data *pgdat, sc->reclaim_idx, 0)) return false; =20 - if (compaction_suitable(zone, sc->order, sc->reclaim_idx)) + if (compaction_suitable(zone, sc->order, sc->reclaim_idx, 0)) return false; } =20 @@ -6043,7 +6043,7 @@ static inline bool compaction_ready(struct zone *zone= , struct scan_control *sc) return true; =20 /* Compaction cannot yet proceed. Do reclaim. */ - if (!compaction_suitable(zone, sc->order, sc->reclaim_idx)) + if (!compaction_suitable(zone, sc->order, sc->reclaim_idx, 0)) return false; =20 /* --=20 2.7.4