RE: (2) [PATCH] fs: fat: add check for dir size in fat_calc_dir_size

[AMIT SAHRAWAT]

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>ÂThereÂareÂmanyÂimplementationÂthatÂdoesn'tÂfollowÂtheÂspecÂstrictly.ÂAnd
>ÂwhenÂIÂtestedÂinÂpast,ÂWindowsÂalsoÂallowedÂtoÂreadÂtheÂdirectoryÂbeyond
>ÂthatÂlimit.ÂIÂcan'tÂrecallÂthoughÂifÂthereÂisÂinÂrealÂcaseÂorÂjustÂtest
>ÂcaseÂthough.
>>>ÂThanksÂOgawa,ÂyesÂthereÂareÂmanyÂimplementations,ÂpreferablyÂgoingÂaroundÂwithÂdifferentÂvariants.
>ÂBut,ÂusingÂstandardÂlinuxÂversionÂonÂtheÂsystemsÂandÂhavingÂsuchÂUSBÂconnectedÂonÂsuchÂsystemsÂisÂintroducingÂissues(importantlyÂbecauseÂtheseÂbeingÂusedÂonÂWindowsÂalsoÂbyÂusers).
>ÂIÂamÂnotÂsure,ÂifÂthisÂisÂsomethingÂwhichÂisÂnewÂfromÂWindowsÂpart.
>ÂBut,ÂsurelyÂextendingÂtheÂdirectoryÂbeyondÂlimitÂisÂcausingÂregressionÂwithÂFATÂusageÂonÂlinux.
Â
regressionÂfromÂwhat?
Â
>ÂItÂisÂmakingÂFATÂfilesystemÂrelatedÂstorageÂvirtuallyÂunresponsiveÂforÂminutesÂinÂtheseÂcases,
>ÂandÂimportantlyÂkeepÂonÂputtingÂpressureÂonÂmemoryÂdueÂtoÂincreasingÂbufferÂheadsÂ(alreadyÂaÂknownÂoneÂwithÂFATÂfs).
Â
I'mÂconfused.ÂWhatÂhappenÂactually?ÂNowÂlooksÂlikeÂyouÂareÂsayingÂthe
issueÂisÂextendingÂsizeÂbeyondÂlimit.ÂButÂpreviouslyÂitÂsaidÂtheÂcorruption.
Â
AreÂyouÂsayingÂ"beyondÂthatÂlimit"ÂisÂtheÂfsÂcorruption?
Â
I.e.ÂdidÂyouÂmetÂrealÂdirectoryÂcorruption?ÂorÂyouÂareÂtryingÂtoÂlimit
becauseÂslownessÂonÂbigÂdirectory?
>>> Will try to arrange the fsck/chkdsk output for the related to disk, to highlight the concerns.

Â
>ÂSoÂifÂthereÂisÂnoÂstrongÂreasonÂtoÂapplyÂtheÂlimit,ÂIÂdon'tÂthinkÂitÂis
>ÂgoodÂtoÂlimitÂit.Â
>>>ÂTheÂreasonÂforÂusÂtoÂshareÂthisÂisÂbecauseÂofÂtheÂunresponsiveÂbehaviourÂobservedÂwithÂFATÂfsÂonÂourÂsystems.
>ÂThisÂisÂnotÂaÂnewÂissue,ÂweÂhaveÂbeenÂobservingÂthisÂforÂquiteÂsometimeÂ(mayÂbeÂaroundÂ1year+).
>ÂFinally,ÂweÂgotÂholdÂofÂdiskÂwhichÂisÂmakingÂthisÂ100%Âreproducible.
>ÂWeÂthoughtÂofÂapplyingÂthisÂtoÂtheÂmainline,ÂasÂourÂFATÂisÂalignedÂwithÂmainÂkernel.
Â
SoÂwhatÂwasÂtheÂrootÂcauseÂofÂslownessÂonÂbigÂdirectory?
>>> Root cause was the continous FAT chain walk through for that directory and making the corresponding applications to stuck.
It keeps going on, so eventually the application had to be terminated.
May be arraning corresponding metadata dump related with this might help in clearing doubts.
I Hope to arrange them soon.
Â
Thanks.
--Â
OGAWAÂHirofumiÂ<hirofumi@xxxxxxxxxxxxxxxxxx>
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