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[Antonis Sidiropoulos]

Den me mperdepses katholou (isws ligo - apo tin apopsi tou giati to 
sxediasan etsi :-).

Oraios. OK. Eftaristw poly gia to xrono pou dietheses.
Twra ksekatharizoun merika pragmata..

A.

V13 wrote:

>On Wednesday 17 September 2003 14:13, Antonis Sidiropoulos wrote:
>  
>
>>Mia pou efere i koubenta prin sxetika me to top:
>>Ti akribws einai to cached memory kai buffered memory pou dixnei?
>>
>>Ypothetw oti to cache einai h klasiki cache tou file system
>>kai to buffered einai to synolo twn buffers pou exoun oi diafores
>>processes (pou prokyptoun apo printf kai tetoia, pou pernoun apo buffer).
>>    
>>
>
>Oxi.. Ta stixia poy blepeis stin free einai toy kernel. Oi buffers poy 
>anafereis gia ta processes (tis printf klp) ylopoioyntai meso tis glibc kai 
>einai 
>a) proeretikoi (sxetiko ayto), 
>b) user-level / per-process
>
>Ta parakato mporei na einai anakribi:
>
>Oi buffers einai ta raw blocks poy diabazei apo toys diskoys. An p.x. baleis 
>mesa ena CD kai to diabaseis olo sector by sector oi buffers soy tha 
>ayksithoyn.
>
>H cache xorizetai se 2: Sthn 'geniki' cache kai sthn swap cache.
>
>H 'geniki' cache exei na kanei me arxeia pleon kai oxi me raw blocks. 
>
>H swap cache einai h cache toy swap. Otan yparxoyn dedomena mesa sto swap ta 
>opoia yparxoyn kai stin mnimi kai DEN einai 'dirty' (se polla eisagogika 
>ayto) (diladi otan ston disko kai sti mnimi exei akribos ta idia), tote h 
>mnimi ayti onomazetai swap cache kai einai apla boithitiki.. mporei na 
>apodesmeytei xoris deyteri skepsi.
>
>=====
>
>Stin praksi tora... (poio low-level) 
>
>Min nomiseis oti paei disk -> buffers -> cache -> user....
>
>Paei disk -> cache/buffers -> user
>
>Otidipote diabazeis apo to disko einai cache/buffers... (ston kernel 
>onomazetai page cache)
>
>Oti exei na kanei me to swap einai swapcache. 
>
>Oti exei na kanei me arxeia, opos read, mmap klp klp onomazetai cache. 
>Stin cache apothikevontai kai alla pragmata opos h cache gia ta inodes, ta 
>dirs k.a. (Den ksero pia akribos, alla nomizo einai otidipote thelei na kanei 
>kapoioy eidoys caching)
>
>=====
>
>one more time:
>
>Otan diabazeis kati apo to disko einai page cache gia ton kernel kai 
>taytoxrona kai buffers. An prokeitai gia file read h kati allo to opoio kanei 
>caching (ektos apo raw block i/o) to metonomazei se cache.
>
>p.x:
>* An kaneis dd if=/dev/hda of=/dev/null tote h cache soy den tha alaksei 
>katholoy eno oi buffers soy tha ayksithoyn. 
>* An kaneis cat /vmlinuz > /dev/null tote tha megalosei h cache soy.
>
>An deis to linux/fs/proc/proc_misc.c ayta poy anaferei to /proc/meminfo einai:
>
>buffers: i.bufferram,
>cache: get_page_cache_size()-total_swapcache_pages-i.bufferram
>swapcache: total_swapcache_pages
>
>ap'opoy fainetai oti yparxei h page cache kai san cache anaferetai h 
>page_cache meion tin swapcache kai toys buffers.
>
>Gia toy logoy to alithes, sto linux/Documentation/filesystems/proc.txt leei:
>
>(perigrafontas to /proc/meminfo)
>     Buffers: Relatively temporary storage for raw disk blocks
>              shouldn't get tremendously large (20MB or so)
>      Cached: in-memory cache for files read from the disk (the
>              pagecache).  Doesn't include SwapCached
>  SwapCached: Memory that once was swapped out, is swapped back in but
>              still also is in the swapfile (if memory is needed it
>              doesn't need to be swapped out AGAIN because it is already
>              in the swapfile. This saves I/O)
>
>  
>
>>Se ena allo omws mixanaki me 2 CPUs, koitakste:
>>  4:42pm  up 1 day,  2:12,  4 users,  load average: 0.07, 0.04, 0.01
>>85 processes: 83 sleeping, 1 running, 1 zombie, 0 stopped
>>CPU states:  0.1% user,  1.2% system,  0.0% nice, 98.5% idle
>>Mem:  776728K av, 744988K used,  31740K free,  30936K shrd, *410828K buff*
>>Swap: 1004020K av,   6008K used, 998012K free                185044K cached
>>
>>410MB buffered.... Poso fysiologiko einai auto re paidia?
>>kai malista se katastasi ousiastika ypnou, xwris na trexei kati sobaro,
>>ektos apo
>>ena http,mysql kai sendmail ...
>>    
>>
>
>To mixanima ayto exei poly mnimi kai den tin xrisimopoiei.. oi buffers poy 
>fainontai mporei na einai etsi gia poly kairo. Mipos etrekse kanena fsck otan 
>ekane boot ?
>
>  
>
>>A.
>>    
>>
><<V13>>
>
>p.s. Elpizo na min se mperdepsa
>  
>

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