Date: Sun, 24 Mar 2013 00:10:39 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: alc@freebsd.org Cc: arch@freebsd.org, David Wolfskill <david@catwhisker.org> Subject: Re: VM_BCACHE_SIZE_MAX on i386 Message-ID: <20130323221039.GO3794@kib.kiev.ua> In-Reply-To: <CAJUyCcMXysO95CqxtWnbkzU5nJx757ktijQi6D%2BUEU5BE=z91g@mail.gmail.com> References: <20130323211001.GN3794@kib.kiev.ua> <CAJUyCcMXysO95CqxtWnbkzU5nJx757ktijQi6D%2BUEU5BE=z91g@mail.gmail.com>
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--f6rhCtP010UFPtiN Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Sat, Mar 23, 2013 at 04:49:06PM -0500, Alan Cox wrote: > The additional KVA that we had to reserve for the vm_page radix tree nodes > already got me thinking about VM_BCACHE_SIZE_MAX a couple weeks ago. With > the extra KVA pressure that is inherent to PAE, e.g., a larger vm_page > struct, we really can't afford to allow the buffer map KVA allocation to > grow much beyond what it would be for a 4GB machine anyway. Moreover, your > work makes the size of the buffer map less important, because it will see > decreasing use as drivers are converted to allow unmapped I/O. So, I would > encourage you to simply use the same cap based on a 4 GB machine for both > PAE and !PAE. I did not checked it, but isn't default PAE config splits user/kernel on the 2GB boundary ? This makes the KVA pressure on PAE less severe, but user mode should be not very happy. Currently, the number of the regular buffer headers allocated is equal to the size of the buffer map / BKVASIZE still. This could be changed now, I believe that Peter' testing fixed most of the bugs in the handling of the maxbufspace. I was too coward to make this change together with the rest of the work. But it could indeed be useful, since buffer map is used only by the metadata buffers for UFS. I did changed VM_BCACHE_SIZE_MAX as you suggested, thanks. http://people.freebsd.org/~kib/misc/i386_maxbcache.2.patch --f6rhCtP010UFPtiN Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iQIcBAEBAgAGBQJRTiheAAoJEJDCuSvBvK1BCDMP/3GQV+rClMKxGms5CLMlXfPW 89UwFQOK896bWe8h26q4Y+OXFiJB+no6L+qf8jPX0N5PK9tyLRwgupB/v/bV4tm1 nUij9sOwxtI2i2ULLwI4QrC/onD9BjiALBxjXLlRQcVUajSgereDK0JCfyfpLDgc qR2lZ/X5GHACRlyzb9/Gw1WkztmBYFS5uzbKtY97jAf0nui/T0XboBE4rFrf1NiE f6kbkYamUkiOz8fLmEERgzHUsU7/JKeuBDuvbDkAd2ZY3G6rE+i3paT7FO1Fyi6g u5P/1pw/9tQ9UBCE5YzDtgVDmclz4oebWd8/PXCr0y3eJZ0m8cyqV45JcYXkkULe 3c9MobHDHtJBQgijWNghXBNswhm8uSuv0pAfOt7mLxS7oPKpEkCycBzNP2DohafO MkLD5noqlKmAtRsp8t7PdZ8e22ziuoQbRCJd8Anrah91ppEYG0+wa6m4MdlvJpsm hHEIJXk+zyEYDXhWawiI0XCHXRzMmGdvq1UylomRxoOVeyGk82fPKFvWBWZHWn8n bvYGqWrHaQ32tLvIeAlE1E+xY5o0yHVeAngqC1Mnp77ADQ0YzT14g2pOIFYDUo02 hlHEDJOuoX9xafl1JowQOGksyC7en4qmK0umBR/4J70RiIgFGrwjNhT9uWt8j06U nOvUcPzX7qUc93OVb1hm =P9+l -----END PGP SIGNATURE----- --f6rhCtP010UFPtiN--
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