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authorhttps://me.yahoo.com/a/g3Ccalpj0NhN566pHbUl6i9QF0QEkrhlfPM-#b1c14 <diana@web>2015-02-16 20:08:03 +0100
committerGNU Hurd web pages engine <web-hurd@gnu.org>2015-02-16 20:08:03 +0100
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-[[!meta copyright="Copyright © 2011, 2012 Free Software Foundation, Inc."]]
-
-[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
-id="license" text="Permission is granted to copy, distribute and/or modify this
-document under the terms of the GNU Free Documentation License, Version 1.2 or
-any later version published by the Free Software Foundation; with no Invariant
-Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license
-is included in the section entitled [[GNU Free Documentation
-License|/fdl]]."]]"""]]
-
-[[!tag open_issue_gnumach]]
-
-[[!toc]]
-
-
-# IRC, freenode, #hurd, 2011-11-28
-
- <braunr> youpi: would you find it reasonable to completely disable the page
- cache in gnumach ?
- <braunr> i'm wondering if it wouldn't help make the system more stable
- under memory pressure
- <youpi> assuming cache=writeback in gnumach?
- <youpi> because disabling the page cache will horribly hit performance
- <braunr> no, it doesn't have anything to do with the host
- <braunr> i'm not so sure
- <braunr> while observing the slab allocator, i noticed our page cache is
- not used that often
- <youpi> eeh?
- <youpi> apart from the damn 4000 limitation, I've seen it used
- <youpi> (and I don't why it wouldn't be used)
- <youpi> (e.g. for all parts of libc)
- <youpi> ah, no, libc would be kept open by ext2fs
- <braunr> taht's precisely because of the 4k limit
- <youpi> but e.g. .o file emitted during make
- <braunr> well, no
- <youpi> well, see the summary I had posted some time ago, the 4k limit
- makes it completely randomized
- <youpi> and thus you lose locality
- <braunr> yes
- <youpi> but dropping the limit would just fix it
- <braunr> that's my point
- <youpi> which I had tried to do, and there were issues, you mentioned why
- <youpi> and (as usual), I haven't had anyu time to have a look at the issue
- again
- <braunr> i'm just trying to figure out the pros and cons for having teh
- current page cache implementation
- <braunr> but are you saying you tried with a strict limit of 0 ?
- <youpi> non, I'm saying I tried with no limit
- <youpi> but then memory fills up
- <braunr> yes
- <youpi> so trying to garbage collect
- <braunr> i tried that too, the system became unstable very quickly
- <youpi> but refs don't falldown to 0, you said
- <braunr> did i ?
- <youpi> or maybe somebody else
- <youpi> see the list archives
- <braunr> that's possible
- <braunr> i'd imagine someone like sergio lopez
- <youpi> possibly
- <youpi> somebody that knows memory stuff way better than me in any case
- <braunr> youpi: i'm just wondering how much we'd loose by disabling the
- page cache, and if we actually gain more stability (and ofc, if it's
- worth it)
- <youpi> no idea, measures will tell
- <youpi> fixing the page cache shouldn't be too hard I believe, however
- <youpi> you just need to know what you are doing, which I don't
- <youpi> I do believe the cache is still at least a bit useful
- <youpi> even if dumb because of randomness
- <youpi> e.g. running make lib in the glibc tree gets faster on second time
- <youpi> because the cache wouldbe filled at least randomly with glibc tree
- stuff
- <braunr> yes, i agree on that
- <youpi> braunr: btw, the current stability is fine for the buildds
- <youpi> restarting them every few days is ok
- <youpi> so I'd rather keep the performance :)
- <braunr> ok
-
-
-# [[gnumach_page_cache_policy]]