From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 764A76C6DF for ; Thu, 14 Dec 2023 23:19:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="amm0jq7w" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=ZpX9OyVmsooR71iBff+A80aL9guypQAVqM/obfLf98M=; b=amm0jq7wabv6SCHJhqIwRv3xPy EhUiM5cB2+Mjp9HMu+G06vCXsQd+tfcx1bcc5YchcZUIx4FAVV0VzJgtdOyF7nFY4RBoXHfETMalt szimEYe3iSqfh18Z3K6MQUeC7xw8/TMbgkaCoAkbcNgzFKsCmTdFAMm1242vXq7KG0jckxr+OFecQ 0SCv+yThDYGMAeJwV8aVJI291SXmmnOOOX1SfRoOBi6e58aRNjHxJ9KafSsxGlxsM6nHptHuGAIoA mxgOMDplG5KBG5Pj7lz5E5Twy0ZMVZ92+3q7Eee/CbeZNJDbEfx2+C1gYASFKeqNK+VJMPUir0zpu A5Fb++zQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1rDuhM-00B27e-Vk; Thu, 14 Dec 2023 23:00:57 +0000 Date: Thu, 14 Dec 2023 23:00:56 +0000 From: Matthew Wilcox To: Jianfeng Wang Cc: akpm@linux-foundation.org, tim.c.chen@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm: remove redundant lru_add_drain() prior to unmapping pages Message-ID: References: <20231214222717.50277-1-jianfeng.w.wang@oracle.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231214222717.50277-1-jianfeng.w.wang@oracle.com> On Thu, Dec 14, 2023 at 02:27:17PM -0800, Jianfeng Wang wrote: > When unmapping VMA pages, pages will be gathered in batch and released by > tlb_finish_mmu() if CONFIG_MMU_GATHER_NO_GATHER is not set. The function > tlb_finish_mmu() is responsible for calling free_pages_and_swap_cache(), > which calls lru_add_drain() to drain cached pages in folio_batch before > releasing gathered pages. Thus, it is redundant to call lru_add_drain() > before gathering pages, if CONFIG_MMU_GATHER_NO_GATHER is not set. > > Remove lru_add_drain() prior to gathering and unmapping pages in > exit_mmap() and unmap_region() if CONFIG_MMU_GATHER_NO_GATHER is not set. > > Note that the page unmapping process in oom_killer (e.g., in > __oom_reap_task_mm()) also uses tlb_finish_mmu() and does not have > redundant lru_add_drain(). So, this commit makes the code more consistent. Shouldn't we put this in __tlb_gather_mmu() which already has the CONFIG_MMU_GATHER_NO_GATHER ifdefs? That would presuambly help with, eg zap_page_range_single() too. > Signed-off-by: Jianfeng Wang > --- > mm/mmap.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 1971bfffcc03..da0308eef435 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -2330,7 +2330,10 @@ static void unmap_region(struct mm_struct *mm, struct ma_state *mas, > struct mmu_gather tlb; > unsigned long mt_start = mas->index; > > + /* Defer lru_add_drain() to tlb_finish_mmu() for the ifndef case. */ > +#ifdef CONFIG_MMU_GATHER_NO_GATHER > lru_add_drain(); > +#endif > tlb_gather_mmu(&tlb, mm); > update_hiwater_rss(mm); > unmap_vmas(&tlb, mas, vma, start, end, tree_end, mm_wr_locked); > @@ -3300,7 +3303,10 @@ void exit_mmap(struct mm_struct *mm) > return; > } > > + /* Defer lru_add_drain() to tlb_finish_mmu() for the ifndef case. */ > +#ifdef CONFIG_MMU_GATHER_NO_GATHER > lru_add_drain(); > +#endif > flush_cache_mm(mm); > tlb_gather_mmu_fullmm(&tlb, mm); > /* update_hiwater_rss(mm) here? but nobody should be looking */ > -- > 2.42.1 > >