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Re: Should diskfs_file_update be called in every io_write?

From: Thomas Bushnell, BSG
Subject: Re: Should diskfs_file_update be called in every io_write?
Date: Tue, 13 Sep 2011 12:57:44 -0700

I think this could also create extra churn, by scheduling a lot of disk writes when a series of writes are done all at once to a single file.

Traditionally, this is addressed by the every-30-seconds update task; there is no expectation of an indefinitely postponed write.

However, much could be improved in this area. Ideally, writes would happen at a smoothly increasing rate as page pressure increased; and ideally, the kernel would be correctly detected sequential access patterns and paging out finished pages speedily on its own.


On Tue, Sep 13, 2011 at 12:50 PM, Sergio López <slpml@sinrega.org> wrote:

Currently, libdiskfs:io_write.c only calls "diskfs_file_update(struct
node *np, int wait)" if the node has been opened with O_FSYNC or if
the entire translator is operating synchronously (diskfs_synchronous
== 1). I think calling diskfs_file_update (with wait == 0) when
working asynchronously could help to reduce pageout pressure during
large I/O operations (except if those operations are being generated
by a mmap'ed file), at the expense of losing the ability of
indefinitely delaying the actual write.

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