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AFNElJ+OAdE1zfH5WCU8l3zdlKUgnmWhYdPCcdP0LyTMTQLS/JClmCeT4Q/mHBKyXkwSZqqVkKaOo2RGuA==@kvack.org X-Gm-Message-State: AOJu0Yws2BImEXs6mXfwSI3tmZ1enBzJIvepmEzSgsaQo8yMPR/w8mf7 yiN57EWyEIlkvnKlcnMLjm4Po3/TmBfvvRPl9bkE2WRLUhXYo0Nq+qq9m8dZhAIudPAZheEZ4Xh KjSIU8A== X-Received: from dlbqs4.prod.google.com ([2002:a05:7023:d04:b0:12c:8bfc:84e3]) (user=fmayle job=prod-delivery.src-stubby-dispatcher) by 2002:a05:7022:2510:b0:11b:f056:a19b with SMTP id a92af1059eb24-12deac72761mr3014031c88.18.1777598376170; Thu, 30 Apr 2026 18:19:36 -0700 (PDT) Date: Thu, 30 Apr 2026 18:19:07 -0700 Mime-Version: 1.0 X-Mailer: git-send-email 2.54.0.545.g6539524ca2-goog Message-ID: <20260501011908.3630802-1-fmayle@google.com> Subject: [PATCH 1/1] mm/readahead: simplify page_cache_ra_unbounded loop counter reset From: Frederick Mayle To: Matthew Wilcox Cc: android-mm@google.com, kernel-team@android.com, Frederick Mayle , Jan Kara , Andrew Morton , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: ADBA6180011 X-Stat-Signature: jzno9tpe95dz9gr7juwa3dzwgne6xxmq X-Rspam-User: X-HE-Tag: 1777598377-650741 X-HE-Meta: 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 0q6EUUqe 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Minor cleanup, no behavior change intended. `read_pages` ensures that `ractl->_nr_pages` is zero before it returns, so the `ractl->_nr_pages` term in these expressions contributes nothing. This seems to have been true since the statements were introduced in commit f615bd5c4725f ("mm/readahead: Handle ractl nr_pages being modified"). The new expression has an intuitive explanation. When filesystems perform readahead, they increment `ractl->_index` by the number of pages processed, so, after `read_pages` returns, `ractl->_index` points to the first page after those already processed. `index` points to the first page considered in the loop. So, `ractl->_index - index` is the number of pages processed by the loop so far. Signed-off-by: Frederick Mayle --- mm/readahead.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/readahead.c b/mm/readahead.c index 7b05082c89ea..b44f13ce5935 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -270,7 +270,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl, */ read_pages(ractl); ractl->_index += min_nrpages; - i = ractl->_index + ractl->_nr_pages - index; + i = ractl->_index - index; continue; } @@ -286,7 +286,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl, break; read_pages(ractl); ractl->_index += min_nrpages; - i = ractl->_index + ractl->_nr_pages - index; + i = ractl->_index - index; continue; } if (i == mark) base-commit: 88ca94c8849696985b1b70ebec4b01c4b58cafdd -- 2.54.0.545.g6539524ca2-goog