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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1rDyWr-00Cl0h-Gv; Fri, 15 Dec 2023 03:06:21 +0000 Date: Fri, 15 Dec 2023 03:06:21 +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> <9792a7f5-62cd-45e1-b7d6-406592cc566d@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9792a7f5-62cd-45e1-b7d6-406592cc566d@oracle.com> X-Rspam-User: X-Stat-Signature: 3498c7odb4meyd5gp8ikh7z1zurnf7ib X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: BCB6FC000A X-HE-Tag: 1702609590-65129 X-HE-Meta: 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 YdHhFWjw AR43jXE1x8RyuBh0LG2wrACwGjeTrHVuD+G+rUraFem1FIqKR1om18g3mWLelW6lw+E+d+/KWrwYMGW2xF9LU005zRFc8ohuri60xS2tTtMeLxNRb08/rOFBTZidMHj+FI85S9PMUAg3kzjOhww1V6ypRxI7HLphxz/+TAJXb7qbJyzwtcPvi0KMjvA== 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, Dec 14, 2023 at 03:59:00PM -0800, Jianfeng Wang wrote: > On 12/14/23 3:00 PM, Matthew Wilcox wrote: > > 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. > > > > Thanks. It makes sense to me. > This commit is motivated by a workload that use mmap/unmap heavily. > While the mmu_gather feature is also used by hugetlb, madvise, mprotect, > etc., thus I prefer to have another standalone commit (following this one) > that moves lru_add_drain() to __tlb_gather_mmu() to unify these cases for > not making redundant lru_add_drain() calls when using mmu_gather. That's not normally the approach we take.