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From: Jeff Moyer <jmoyer@redhat.com>
To: =?utf-8?B?6Z+p56OK?= <bonben1989@gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: About read/write requests in IO scheduler
References: <CAK2Ky6wEUDS0bQbbYSKv+hX=f6sCjJM7Fu4zOzAR_ftVX1obUg@mail.gmail.com>
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Date: Mon, 11 Nov 2013 13:32:24 -0500
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韩磊 <bonben1989@gmail.com> writes:

> In IO scheduler level, whether all the read requests are synchronous?

Generically, yes, I/O schedulers (and the whole block layer, in fact)
consider READs synchronous:

/*
 * We regard a request as sync, if either a read or a sync write
 */
static inline bool rw_is_sync(unsigned int rw_flags)
{
        return !(rw_flags & REQ_WRITE) || (rw_flags & REQ_SYNC);
}