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    SubjectRe: [PATCH] Remove process freezer from suspend to RAM pathway
    Date
    Am Donnerstag, 5. Juli 2007 schrieb Pavel Machek:
    > On Tue 2007-07-03 19:20:59, Oliver Neukum wrote:
    > > Am Dienstag, 3. Juli 2007 schrieb Rafael J. Wysocki:
    > > > On Tuesday, 3 July 2007 15:08, Rafael J. Wysocki wrote:
    > > > > On Tuesday, 3 July 2007 07:51, Benjamin Herrenschmidt wrote:
    > > > > > On Tue, 2007-07-03 at 05:29 +0100, Matthew Garrett wrote:
    > > > > > > Suspend to RAM on a machine with / on a fuse filesystem turns out to be
    > > > > > > a screaming nightmare - either the suspend fails because syslog (for
    > > > > > > instance) can't be frozen, or the machine deadlocks for some other
    > > > > > > reason I haven't tracked down. We could "fix" fuse, or alternatively we
    > > > > > > could do what we do for suspend to RAM on other platforms (PPC and APM)
    > > > > > > and just not use the freezer.
    > > > > >
    > > > > > The main reason for deadlocks is because we do a sys_sync() after the
    > > > > > freeze, which we shouldn't do.
    > > > >
    > > > > So why don't we remove the sys_sync() from freeze_processes() instead?
    > > >
    > > > The patch follows (untested).
    > > >
    > > > Greetings,
    > > > Rafael
    > > >
    > > >
    > > > ---
    > > > From: Rafael J. Wysocki <rjw@sisk.pl>
    > > >
    > > > We shouldn't sync filesystems from within the freezer, because it's not needed
    > > > for suspend to RAM and leads to problems with FUSE.
    > >
    > > This seems fishy. Swsusp needs enough clean memory to make enough
    > > room for the image. If you sync before you freeze, the running tasks can
    > > redirty memory.
    > > What makes you sure that you don't die as shrink_all_memory() writes out
    > > pages?
    >
    > Shrink_all_memory should just free enough memory, what's the problem?
    > Yes, we can have dirty memory, shrink_all_memory() can write that out
    > just fine.

    If there's any dirty memory to be written out through fuse, this will not
    work as user space is already frozen. Now I am told that with fuse writes
    are synchronous. Therefore I don't understand why having a call to sys_sync()
    can make a difference. IMHO removing it to make fuse work covers over
    a symptom but hides the bug.

    Regards
    Oliver

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