From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.79 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794220507; b=vYokc8IjpmNgVO3j6Aa15I4OutlJojbsOMvP6v/uL2UlKyfhEOz3TUsC+Y/7OPooY6RR tu7qgdaDVsTmrM9DmBGqcFRZCuulnVo2gbf/TAmE1xag5NhWrIXtyTTmoukTMavU50xhv zvdTEf9Peeay98gDOuLcPMAtgYVV2NyyilUjpJC3NFIxFJTIDP19wJcqJKXcmqqsA/i7H lL5BC+U6x2LbJc8/1mz486fWohZwxyunQQR/48kzxTKyvk9oBKK6Tk5mopH+GOAGlBF3i yE7Xt0+DBSt76rQiFlRdJJDLvMa1JQe1EpWo48+pE5zqNZauwPfZBksItVz4GPnyONg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794220507; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:Date:Subject:MIME-Version: Content-Type:Content-Transfer-Encoding:Message-Id:References: In-Reply-To:To:Cc:X-Mailer; bh=DsGtn4KFPLGuAk1q5B2pREh+sGKflm9tEnT1EFIbPjA=; b=D1s9kmYsl0lCgeGAwdzahNeU7N2dkB39WKKKKSQumXVPKTqDsqOnWOyHUzntfFNBZuyI Pb7rYykZaue/RoRa7sJP0AOArz3OBOdVv86vIlVHpvmL2cI1YYniiXcqVbbUBOf7Y5HhM J36Q3lfncEgxWWmYetqd0kAZabaO5zCMJWtDBhj9Zi7X8cd4/snp7urpJ1c55GPnEeIBE U/SF0Yg+4VofdkUtu54tz5HPkJUU7JOaEz9klILpeCbuslnHl0pZ7RoPMexwNThppXXkn RiHLK/YttzRxxzRPuLZdPQEi5IAPboxJwFxjMACEloh2V8aIPPdukWfZHXnNcUGQJjg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=LsCCK+Ye; arc=none smtp.remote-ip=95.215.58.79 Received: from mta1.migadu.com (out-79.mta1.migadu.com [95.215.58.79]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 10855606A323 for ; Mon, 9 Nov 2026 10:35:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 10855606A323 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=LsCCK+Ye X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=bCU29ep+uwz6VaIaH7VVMUYbRv38UnA4EsVYxT/9pjs=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1794220504; v=1; x=1794825304; b=LsCCK+YeiL7Ml+HbL21XCdTjqFj5x9+iCSUBFlkzlrluAahWpau7tAgMULaETmvvtrlZlbvf WCsveD3qUjSdIZ0yTKnteI14Zbj66IspTGnOG3N9agJKcXJK4NFahMp01PkGqGBxHEKywDuRXF5 yFHshJQh1OBTwaXxbP4jUfxk= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 29236d32ff73c5e8; Mon, 09 Nov 2026 10:35:04 +0000 X-Mizu-Trace-ID: 29236d32ff73c5e8 X-Migadu-Flow: FLOW_OUT From: Qiliang Yuan Date: Mon, 09 Nov 2026 05:34:13 -0500 Subject: [PATCH v2 3/3] mm/filemap: extend VM_SEQ_READ readahead below descending faults X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261109-bug-mm-mmap-readahead-descending-v2-3-abac52890a9c@linux.dev> References: <20261109-bug-mm-mmap-readahead-descending-v2-0-abac52890a9c@linux.dev> In-Reply-To: <20261109-bug-mm-mmap-readahead-descending-v2-0-abac52890a9c@linux.dev> To: "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton , Vishal Moola , fujunjie Cc: Roman Gushchin , Usama Arif , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qiliang Yuan X-Mailer: b4 0.13.0 On a VM_SEQ_READ mapping, a synchronous fault reads ahead from the faulting page towards higher offsets through page_cache_sync_ra(). A reader that moves towards lower offsets, such as memmove() copying backwards out of a mapping, finds the pages above the fault already cached, so each of its faults reads a single new page. page_cache_sync_ra() also looks for a stream only below the fault and takes it for a small random read. When the page above the fault is already cached, read the window of ra_pages that ends at the faulting page instead, without a readahead mark. Reading one byte from each page of a 2 GiB file, last page first, in a MADV_SEQUENTIAL mapping with a cold page cache, read_ahead_kb 8192: before after time 50.92 s 0.96 s major faults 524289 258 Signed-off-by: Qiliang Yuan --- mm/filemap.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/mm/filemap.c b/mm/filemap.c index e445279cc561f..be587f8d0e8e6 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3405,7 +3405,19 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) if (vm_flags & VM_SEQ_READ) { fpin = maybe_unlock_mmap_for_io(vmf, fpin); - page_cache_sync_ra(&ractl, ra->ra_pages); + if (!filemap_descending(mapping, vmf->pgoff, 1)) { + page_cache_sync_ra(&ractl, ra->ra_pages); + return fpin; + } + /* Read the window that ends at the faulting page */ + ra->start = vmf->pgoff + 1 - + min_t(unsigned long, ra->ra_pages, + vmf->pgoff + 1); + ra->size = vmf->pgoff + 1 - ra->start; + ra->async_size = 0; + ra->order = 0; + ractl._index = ra->start; + page_cache_ra_order(&ractl, ra); return fpin; } } -- 2.43.0