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Message-ID: <bf1ca326b432444e7d97cac7210e07d2a4ea7fcf.camel@gmail.com>
Date: Fri, 11 Sep 2020 13:35:23 +0200
From: Bean Huo <beanhuo.cn@...il.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, beanhuo@...ron.com,
Richard Weinberger <richard@....at>
Subject: Re: [PATCH RFC] mm: Let readahead submit larger batches of pages
in case of ra->ra_pages == 0
On Fri, 2020-09-11 at 10:47 +0100, Christoph Hellwig wrote:
> > Hi Andrew
> > Sorry, I am still not quite understanding your above three
> > questions.
> >
> > Based on my shallow understanding, ra_pages is associated with
> > read_ahead_kb. Seems ra_pages controls the maximum read-ahead
> > window
> > size, but it doesn't work when the requested size exceeds
> > ra_pages.
> >
> > If I set the read_ahead_kb to 0, also, as Christoph mentioned, MTD
> > forcibly sets ra_pages to 0. I think the intention is that only
> > wants
> > to disable read-ahead, however, doesn't want
> > generic_file_buffered_read() to split the request and read data
> > with
> > 4KB chunk size separately.
>
> They way I understood Richard this is intentional.
Hi Christoph
Thanks. understood now, MTD expects this result. Even so, I think this
patch doesn't impact MTD because the flash-based FS only achieved the
readpage. Inside __do_page_cache_readahead will use mapping->a_ops-
>readpage to read data.
Thanks,
Bean
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