Difficult with some tunes, but A minor is easy enough to play. The Galloglass Jig comes to mind. The Dusty Windowsill is another.
According to all the sources I see, Dusty Windowsill is A dorian.
Gallowglass (which I’ve never learned) appears to be in A melodic minor or something wacky like that – it’s got Fs and Gs both sharp and natural. I don’t know what to make of it, I’ve seen nothing else like it in Irish music. (According to the Fiddler’s Companion, it’s a jig version of “Neil Gow’s Lament for the Death of his Brother”, which might explain that.)
A natural minor has F-naturals throughout, which is why I refered to it as “hard” – it requires half-holing. Obviously this is hard only in a relative sense, as there are dozens if not hundreds of tunes popular with fiddlers which are in equally bad if not worse keys for whistle.
I play Neil Gow’s Lament and use Fnats and F#s. If there’s a G# I don’t remember where it is and obviously don’t use it.
If you are interested, I once did a study of ABC tunebooks and found that dorian tunes far outnumbered aolian tunes. Dorian is the bog standard minor for ITM, it seems.
And on that subject: I conjecture that this is due to the type of instruments people have played. If your instrument plays a 2-octave major scale, you are inclined to use a dorian minor rather than an aolian minor. The dorian is just one step up, and fits the instrument’s range better.
But pick any E “minor” tune and chances are it’s dorian. You can often recognize this in the chord progression that periodically drops a whole step down to D major.
I notice also that the tunes that sound “really Irish” to my ears are ones that contain that whole-step chacha somewhere in the melody, where a phrase repeats in these two keys a whole-step apart. Example: B part of Banish Misfortune, with a phrase in D major, then again in C major (this is D mixolydian mode.)
Caj
I disagree, at least if you go by the notes of the melody. (I don’t want to argue about what chord progressions should be accompanying the tunes!) It’s easy to think of tunes which are in E natural minor – “Dunmore Lasses”, “Fermoy Lasses”, and “Rolling in the Barrel” are classic E reels which have C naturals.
If anything, I think it’s quite possible the majority of E minorish tunes don’t have C in it at all, natural or sharp, except maybe as a passing tone in a triplet.
But B Aeolian is pretty common. It’s interesting, because I find it relatively easy on whistle, but a little clunky on mandolin and fiddle, where I sometimes find myself holding B on the 2nd string and E on the third with one finger in order to play up to speed.
Anyhow, since B is just a whole tone off of A, range will seldom be a sufficient reason to put up with a half-holed F.
I think that Dorian vs. Aeolian is more a question of feeling than of fitting something to an instrument. Dorian-mode is so popular in Appalachian music that people are willing to go to the trouble of retuning the banjo.
Judging by Henrik Norbeck’s tune archive I see about 2 times as many dorian tunes as ones just labeled “minor.”
That’s based on his own classification; Norbeck denotes tunes as dorian or mixolydian in their key fields.
Caj
Another tune that keeps popping up in sessions out here in California is that darn “Gravel Walk”. I guess I’ll have to “bit the bullet” and really learn it. The fiddlers seem to love it, but I find it a bit of a struggle on flute.
This tune gives me fits on the pipes.
I think I’ve heard the gravel walk played on the bagpipes under another name. The rogues of scotland is what I recall. I had it in mind to learn
that one, just haven’t got around to it yet. Does anyone have the dots
for it?
Brilliant tune though. I’ve got the 2nd part down, pretty much. The 4th part is my test piece - if it sounds good, I;m playing well that day. If not (more likely) then I am playing sh!te.
It’s a fiddle tune, so don’t feel too bad! However, it does indeed make an outstanding Holy Grail, especially at speed. 
But don’t worry. You can get 'em back with The Skylark or something. They seem to hate that one.
Yeah - “Gravel Walk” - for me it is more like “Gravel Crawl” (on my belly). For the fiddlers, those octave jumps are simply a bow change from one string to the other, but on the Uilleann pipes, it requires precise bag pressure control. Kinda tricky. And on the flute, it ain’t much better. 
The hard part for me is the C-natural pedal . . .nasty. FOr the 1st & 2nd parts I just tongue the jumps (DOes that sound weird or what?) which might not be authentic but it works. It must be brutal on pipes.
The 78th Fraser Highlanders (GHB band) play a great version of this tune on one of their albums. THey can;t fit the 3rd or 4th parts though.
I know those jumps from the c-nat. I think you might just have to tongue them a bit.