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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pPaCY-000mt8-VE; Wed, 08 Feb 2023 02:28:50 +0000 Date: Wed, 8 Feb 2023 02:28:50 +0000 From: Matthew Wilcox To: coolqyj@163.com Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Qian Yingjin , Andrew Morton Subject: Re: [PATCH] [PATCH V2] mm/filemap: fix page end in filemap_get_read_batch Message-ID: References: <20230208022400.28962-1-coolqyj@163.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230208022400.28962-1-coolqyj@163.com> X-Rspamd-Queue-Id: 853821C000B X-Stat-Signature: 3su9ym3gnmmqhu6zrt45acmgus59ndgz X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1675823337-722797 X-HE-Meta: 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 TJghIwVT j4lqUznELrY9cbmwURGT3BHTst7b3wFt1SFJ6JwNHUezmpZ3m+e/FHC9b7oXlhelgs9XjjBeX695sHRXgdM58JYj1b7pzZtATZ+gHc7JCy/eFRGvwUS4iyF/ia7DO62ne5huoh5VrbelJuYQoRxD+VaHcbmKaUzjSPtTa4d1qrFZMopmjtx35JovjwkhyTehrSIMC4nOJLKSNUqmRLE29Au5Sl7xaN/b9mXDUi+4WJfovy0NdshNeG8S7EQIjCm/uVsQQZjRyECx8kO27OjNuuKpZ6PRKyyEX76ugafgqDb8zBdR9jFExeMtboDbUOi9pojrfNgg2dV1ypXg4+QdM14qVNBLwxgpvLqGKxcC0RY1n06sss+Hc1NOI5+EoaVatNEZZbikoQ6+bd0fHOY52KA5WvFVi/wKgINkkDaXSLL0S02g8g5FreGnt5rEkoLbPVx82EC6GjltVMYGcy1SJ/u1TM6uQUFTq8HDAcrzR8xvReQU= 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: On Wed, Feb 08, 2023 at 10:24:00AM +0800, coolqyj@163.com wrote: > From: Qian Yingjin > > I was running traces of the read code against an RAID storage > system to understand why read requests were being misaligned > against the underlying RAID strips. I found that the page end > offset calculation in filemap_get_read_batch() was off by one. > > When a read is submitted with end offset 1048575, then it > calculates the end page for read of 256 when it should be 255. > "last_index" is the index of the page beyond the end of the read > and it should be skipped when get a batch of pages for read in > @filemap_get_read_batch(). > > The below simple patch fixes the problem. This code was introduced > in kernel 5.12. > > Fixes: cbd59c48ae2b ("mm/filemap: use head pages in generic_file_buffered_read") > Signed-off-by: Qian Yingjin Reviewed-by: Matthew Wilcox (Oracle) Cc: stable@vger.kernel.org > --- > mm/filemap.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/mm/filemap.c b/mm/filemap.c > index c4d4ace9cc70..0e20a8d6dd93 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2588,18 +2588,19 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter, > struct folio *folio; > int err = 0; > > + /* "last_index" is the index of the page beyond the end of the read */ > last_index = DIV_ROUND_UP(iocb->ki_pos + iter->count, PAGE_SIZE); > retry: > if (fatal_signal_pending(current)) > return -EINTR; > > - filemap_get_read_batch(mapping, index, last_index, fbatch); > + filemap_get_read_batch(mapping, index, last_index - 1, fbatch); > if (!folio_batch_count(fbatch)) { > if (iocb->ki_flags & IOCB_NOIO) > return -EAGAIN; > page_cache_sync_readahead(mapping, ra, filp, index, > last_index - index); > - filemap_get_read_batch(mapping, index, last_index, fbatch); > + filemap_get_read_batch(mapping, index, last_index - 1, fbatch); > } > if (!folio_batch_count(fbatch)) { > if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ)) > -- > 2.34.1 >