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Re: Odd pagebuf message

To: Eric Sandeen <sandeen@xxxxxxx>
Subject: Re: Odd pagebuf message
From: Jens Axboe <axboe@xxxxxxx>
Date: Mon, 17 Dec 2001 12:07:45 +0100
Cc: David Chambers <davidc@xxxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx
In-reply-to: <Pine.LNX.4.33.0112161927200.12284-100000@chuckle.americas.sgi.com>
References: <200112161757.fBGHvPW21023@pinga.salk.edu> <Pine.LNX.4.33.0112161927200.12284-100000@chuckle.americas.sgi.com>
Sender: owner-linux-xfs@xxxxxxxxxxx
On Sun, Dec 16 2001, Eric Sandeen wrote:
> Congratulations, you appear to be the world's first user of the
> pre-allocated buffer head pool in pagebuf!  :)
> when pagebuf initializes, it sets aside a handful of buffer heads to use
> in "emergency" situations, i.e. if it tries to allocate a buffer head and
> fails.  If this happens, it takes one from this pre-allocated pool
> instead.  If normal allocation fails, _and_ the pre-allocated pool is
> empty, that thread will sleep until buffer heads get replaced in the
> pre-allocated pool - this is what happened to you.  The thread gets woken
> up and picks up where it left off as soon as it is able to get a
> buffer head allocated from the pool.

BTW, in your 2.5 tree please drop such private pre-allocations and use
the mempool_* interface. bio/bio_vec allocations and highmem are already
using them :-)

Jens Axboe

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