From: Vladislav Bolkhovitin <vst@xxxxxxxx> Subject: Re: Ang: Re: [Stgt-devel] Re: [Iscsitarget-devel] stgt a new version of iscsi target? Date: Sat, 10 Dec 2005 18:32:46 +0300 > >>>Also is the page cache comment in reference to us using the page cache > >>>for our reads and writes or I am not sure why you wrote that if you do > >>>not do it right now. > >> > >>Hm, at first, the page cache already used somehow in fileio dev handler > >>(though, with additional mem copy). At the second, fully utilize the > >>page cache is one of two major improvements that are pending in scst, > >>because it is required changing the kernel, which until some moment try > >>to avoid. Although I prepared what is necessary for that. > >> > >>The idea basically is the following. When READ operation arrives, pages > >>for all requested blocks are at first searched in the page cache > >>(probably, in SIRQ context, because it isn't expensive operation) and if > >>all pages are found, they are referenced and the result will be sent to > >>the initiator. Then the pages will be dereferenced (so, no pages > >>allocation will be done at all). Otherwise, the missed pages will be > >>allocated and the command will be rescheduled to the thread, which will > >>read them. Then, after the response is sent, the pages will remain in > >>the page cache for future accesses. For WRITEs the processing is the > >>similar, the pages with the data will be put in the page cache. > > > > The Ardis iSCSI target code does the same thing. > > Perfectly. So, why don't do it on the mid-layer level where all targets > can benefit from it? Because I think that it not of much performance benefit. - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
